Bombs shattered a bus Thursday and exploded outside a hotel where President Bush is to stay this weekend, back-to-back attacks that killed four people, wounded 17 and heightened security concerns over an upcoming NATO (search) summit.
Authorities said militant leftists were suspected in the blasts in Istanbul, which killed four people and wounded 14, and an earlier attack outside a luxury hotel in Ankara (search) that injured three others, including two police officers. Three suspects were detained in Istanbul, police said.
The blasts were the latest in a series of explosions — most of them small, without casualties — ahead of the summit. Bush arrives in Ankara on Saturday night to meet with Turkish leaders before heading to the summit in Istanbul.
Security is expected to be extremely tight at the Istanbul summit, with more than 23,000 police on duty. Police are using steel and concrete barriers to seal off a zone in the heart of the city, where the conference will take place. Military surveillance aircraft are to monitor the airspace above the meeting.
"Turkey is a strong and secure country. Such incidents take place in New York, in Washington and everywhere else in the world," Foreign Minister Abdullah Gul (search) said after the Ankara blast.
The White House pledged the attacks would not affect Bush's travel plans.
"It does appear that these terrorist attacks are intended to disrupt preparations for the upcoming NATO summit, which is a gathering of free nations united in our global fight against terrorism," said White House press secretary Scott McClellan. "In terms of (Bush's) schedule, nothing has changed."
There is no evidence to suggest the blasts were connected to violence this week in Iraq and Russia, U.S. officials said.
Militant Abu Musab al-Zarqawi (search) claimed responsiblity for Thursday's coordinated attacks in Iraq that killed dozens of people. In the southern Russian republic of Ingushetia, separatist rebels from neighboring Chechnya are believed to be behind assaults that killed nearly 100 people.
The blasts in Istanbul and Ankara came amid growing concerns over security at the NATO summit.
Al Qaeda-linked suicide bombers killed more than 60 people in a series of bombings in November. Militant leftist groups are also active in Turkey, as are Kurdish and Islamic groups.
Scores of people believed to be linked to such groups have been detained in security sweeps in recent weeks.
"The target is Turkey's prestige, Istanbul's prestige," Istanbul Gov. Muammer Guler said. "We will do everything we can to prevent such incidents."
Bush is scheduled to meet Prime Minister Recep Tayyip Erdogan (search) and President Ahmet Necdet Sezer in Ankara on Sunday.
British Prime Minister Tony Blair, French President Jacques Chirac and other NATO leaders will attend the summit that starts Monday.
The Istanbul explosion occurred as the bus was traveling in a residential area, some five miles from the summit area. It tore open the side of the bus and blew out all its windows.
Guler said the bomb exploded in the lap of a woman in her early 20s who was most likely transporting the bomb when it went off prematurely. The woman was killed, he added.
"The target was neither the bus nor the passengers aboard," Guler said.
Guler said the blast was caused by a concussion grenade — a type of bomb that makes a lot of noise but usually causes little damage unless it goes off in a confined area.
Witness Onur Kaval was coming from a pharmacy when he heard the blast in Istanbul.
"I saw smoke coming out of the bus," Kaval said. "I saw people jumping out of the windows. Everyone was crying and was in shock. It was a horrible scene. I saw people without arms and whose feet were ripped off."
Ankara Police Chief Ercument Yilmaz said officers were wounded there when they approached a package containing explosives to verify a tip about a bomb.
One officer lost a foot in the blast, said Adil Surat, head of the trauma unit at Hacettepe University hospital, speaking to the Anatolia news agency.
A small Marxist group, MLKP-FESK (search), claimed responsibility for the Ankara blast, private NTV television reported.
The Ankara bomb exploded some 75 yards from the entrance of the Hilton hotel, shattering windows of nearby buildings.