Suicide bombers carried out nearly simultaneous attacks on three U.S.-based hotels in the Jordanian capital Wednesday night, killing at least 57 people and wounding 115 in what appeared to be an Al Qaeda assault on an Arab kingdom with close ties to the United States.

The explosions hit the Grand Hyatt, Radisson SAS and Days Inn hotels just before 9 p.m. One of the blasts took place inside a wedding hall where 300 guests were celebrating -- joined by a man strapped with explosives who had infiltrated the crowd. Black smoke rose into the night, and wounded victims stumbled from the hotels.

"We thought it was fireworks for the wedding but I saw people falling to the ground," said Ahmed, a wedding guest at the five-star Radisson who did not give his surname. "I saw blood. There were people killed. It was ugly."

Jordan's deputy prime minister, Marwan Muasher, said nobody claimed responsibility but that Abu Musab al-Zarqawi, the Jordanian-born leader of Al Qaeda in Iraq, was a "prime suspect."

A U.S. counterterrorism official, who spoke on condition of anonymity because the investigation is ongoing, said the strong suspicion is that al-Zarqawi was involved because of his known animosity for Jordanian monarchy and the fact that it was a suicide attack, one of his hallmarks.

The Arab satellite TV channels Al-Jazeera and Al-Arabiya on Thursday reported that Al Qaeda had claimed responsibility. The stations did not say how the claim was made.

In February, U.S. intelligence indicated that Usama bin Laden was in contact with al-Zarqawi, enlisting him to conduct attacks outside of Iraq. Jordan has arrested scores of Islamic militants for plotting to carry out attacks and has sentenced many militants to death in absentia, including al-Zarqawi.

Its capital has become a base for Westerners who fly in and out of neighboring Iraq for work. Amman's main luxury hotels downtown are often full of American and British officials and contractors enjoying the relative quiet of the city.

"Obviously this is something Jordan is not used to," Muasher said. "We have been lucky so far in avoiding those incidents." He said most of the casualties appeared to be Jordanians and that authorities had sealed the country's land borders.

A State Department official said there was no information on any American casualties.

The first blast was reported at about 8:50 p.m. at the five-star Grand Hyatt. The explosion took place in the lobby and shattered its stone entrance.

Thousands of shards of broken glass crunched underfoot as hotel bellboys, some bloodied by the blast, ran alongside luggage trolleys being used to transport the wounded.

An American man blurted out in a thick Southern drawl: "My friends are dead."

Steve Olderman, a businessman from England, was attending a business dinner at the Grand Hyatt, where an information technology conference took place earlier in the day.

"Suddenly, we heard an explosion and the whole hotel filled with smoke, and suddenly we found ourselves outside the hotel," said Olderman, who was on the ground floor at the time of the attack.

"We saw bodies lying as we were coming out" of the hotel, said Olderman, who had been staying at the Radisson. "It was pretty horrific. We were sitting beside a huge plate glass window and it just exploded beside us. ... We were lucky to get out alive."

A few minutes after that attack and a short distance away, police reported the explosion at the wedding celebration, which took place in a special reception hall on the ground floor of the Radisson. At least five people were killed and 20 wounded.

The groom, Ashraf al-Akhras, who suffered serious injuries, said both his father and his wife's father were among the dead.

The Radisson is popular with American and Israeli tourists and was a target of several foiled Al Qaeda plots, including a conspiracy to attack U.S. and Israeli tourists during the kingdom's millennium celebrations. No Israeli casualties were reported.

Amin Omar, a concierge at the Radisson, said Jordanian security forces later took over the hotel and that all foreign and local guests were returned to their rooms.

"This is a terrible, terrible situation. The explosion took place during a local Jordanian wedding and caused a lot of damage. Broken chairs, shattered glass, thrown tables," Omar said. "Everything is still in a great fuss."

The third explosion, at the Days Inn, happened after a car packed with explosives approached the hotel, Muasher said. He said the car could not cross a protective barrier so it detonated outside. As a result, the casualties at the Days Inn were not so extensive as at the other hotels, he said.

Muasher reported 57 killed and 115 wounded in the three bombings, with the worst damage was at the Radisson because the suicide bomber got inside the wedding party of Jordanians.

Two Palestinian security officials were among at least four Palestinians killed, Attala Kheri, the Palestinian envoy to Jordan, said on Thursday.

Three Chinese were killed, all from the Defense University of the Chinese People's Liberation Army -- an elite military training university, the Foreign Ministry in Beijing said Thursday.

Chinese President Hu Jintao "strongly condemned" the attack and reiterated that his government firmly opposes terrorism in all its forms, in a telegram to Jordan's King Abdullah II, the ministry said.

There were no visible signs of cracks in the structure of the stone buildings that were attacked and no traces of burned vehicles. But shattered glass and some burned furniture could be seen in two of the targeted hotels, mainly in the wedding banquet hall at the Radisson SAS, where parts of the false ceiling collapsed. SAS is a partner of Radisson in Europe.

In addition to housing Westerners, Amman's hotels have become a gathering spot for affluent Iraqis who have fled their country's violence. Their presence -- and money -- has caused an economic boom and attracted high-priced prostitutes.

The Grand Hyatt has 316 guest rooms and 50 luxury residential apartments in the adjoining Hyatt Tower. The hotel, with a beige-and-cream facade and a shiny gold revolving door, is in the heart of Amman's business and diplomatic district on Hussein Bin Ali Street.

The Radisson has 260 guest rooms. Its main entrance is covered by a white portico with several dozen international flags lining the top.

The three hotels have security guards hired from a private Jordanian firm stationed in the reception areas. Each of the hotels has one or two police cars guarding the buildings around the clock.

King Abdullah II cut short his official visit to Kazakhstan and was returning home.

"The hand of justice will get to the criminals who targeted innocent secure civilians with their cowardly acts," he said in a statement.

The White House said the United States was prepared to offer help in the investigation.

In a statement, Secretary of State Condoleezza Rice said "such wanton acts of murder against innocent people violate every faith and creed." She pledged to Jordan that the U.S. would "stand together, unwavering, to defeat the evil that threatens our people and way of life."

U.N. Secretary-General Kofi Annan, who is on a trip in the Middle East, canceled a scheduled visit to Jordan because of the attacks.

Security forces, including special anti-terror police units, fanned out across the Jordanian capital after the attack. Police swiftly set up road blocks across Amman, where they searched cars and checked passengers' identification.

Special anti-terrorism units in armored vehicles sealed off streets around diplomatic missions, government offices and hotels. Police said Amman was virtually cut off from other cities because all highways leading to the capital were shut.

At midnight, the capital appeared virtually deserted, except from tens of police cars and armored vehicles. Plainclothed security officials were also seen on foot, strolling near the blast sites and stopping motorists to inspect their IDs.

Prime Minister Adnan Badran declared Thursday a national holiday -- apparently in order to allow tightened security measures to take hold.

The date of Wednesday's attack, Nov. 9, would be written as 9/11 in the Middle East, which puts the day before the month. A Jordanian government spokesman declined to speculate on what this means. But Jordanian citizens were sending mobile messages that read: "Have you noticed that today is 9-11, similar to America's 11-9?"

Al-Zarqawi has successfully and unsuccessfully launched attacks against Jordan dating back to the assassination of senior U.S. diplomat Laurence Foley outside his Amman home in October 2002. He is also blamed for a foiled attack on the Jordanian intelligence building and other targets in April 2004.

In a seven-minute audio recording later that month, al-Zarqawi said: "The war has its ups and downs, and as the days go by, we will have more fierce confrontations with the Jordanian government. The chapters of some of these confrontations have ended, but what is coming is more vicious and bitter."