Egypt said Friday that a bomb blast that rocked a Cairo bazaar (search) popular with foreigners may have been carried out by a man working alone as the death toll rose to three after an American tourist died of his wounds.

Another three Americans were among the 18 people injured by the bomber. It was the first such attack in the city in seven years.

Many of the wounded, who included Egyptians, French and a Turk, suffered severe wounds from nails packed in the bomb, which witnesses said appeared to have been set off by a man on a motorcycle.

The attack in the al-Moski bazaar near the al-Azhar mosque (search), one of the most influential institutions in the Sunni Muslim (search) world, came after years of calm since Egypt suppressed Islamic militants, who in the 1990s carried out bombings and shootings against tourists in their campaign to bring down the government.

Egypt's Prime Minister Ahmed Nazief (search) said the explosion may have been carried out by a person working alone but stressed inquiries are ongoing.

"Initial evidence is that it was an individual act. The way in which the explosive was prepared was very primitive," Nazief said after visiting victims at a hospital. "Still, we will await the results of the investigation."

A previously unknown militant group, the Al-Ezz Islamic Brigades, claimed responsibility, saying the attack was a message to Egyptian President Hosni Mubarak that Islamic militancy still exists in his country.

"The reason behind choosing a place like al-Azhar district is that it is known to (attract) many tourists and the tourists whom we surveyed went to this area," the group said in a statement posted on a known Islamist Web site. The statement could not be verified.

Police said they have taken in two people for questioning and were investigating a motorcycle found near the scene with nails scattered around it. Initial investigations suggested the explosive was a homemade nail-packed bomb that went off prematurely, killing the man who was carrying it, according to police.

DNA tests were being conducted on the remains of a man found dead at the scene, the state news agency MENA reported, citing a security official.

Hundreds of police also sealed off a 400-yard stretch of road lined by rundown warehouses and stores where the blast took place, as investigators interviewed shop owners for clues. Blood stains remained on the road and the second-story wall of a building in the bazaar.

Amin al-Laban, a 51-year-old spice store owner, said his 22-year-old son, Mohamed, was injured in the explosion.

"The blast was so big that I thought that the building above my shop collapsed, when I came out to check on Mohamed, I could not see anything from the black dust," the elder al-Laban said.

U.S. Embassy spokeswoman Micaela Schweitzer-Bluhm said an American man died Friday morning of wounds sustained in the blast and confirmed that three others were wounded, but she provided no other details.

The U.S. Embassy in Cairo also issued a statement warning Americans to stay away from Khan al-Khalili, a market connected to al-Moski, and to use prudence elsewhere in the city.

Mohammed Mahdi Akef, the leader of the Muslim Brotherhood, Egypt's largest Islamic group that was outlawed in 1954, denounced the bombing as a "cowardly act" and said it should not be used to "derail" the nation's growing reform movement.

Tourism Minister Ahmed El Maghraby said he had no details on who was responsible for the blast but noted that similar attacks in the past have "turned out to be the act of one individual or a very small group of people."

El Maghraby condemned the attack but also called for calm and said tourists should not be scared away.

The last significant attacks in Cairo were in 1997. That September, two gunmen fired on a tour bus outside the Egyptian Museum in central Cairo, killing 10 people. Two months later, militants killed 62 people in an attack at a pharaonic temple in Luxor.

In October 2004, explosions hit several hotels in the Sinai Peninsula, including one in the resort of Taba, killing 34 people. Egyptian authorities said that attack was linked to Israeli-Palestinian violence.