Turkey bus explosion kills four
ISTANBUL, Turkey (CNN) -- Four people have been killed and at least a dozen injured after a bomb carried by a woman exploded on a bus near Istanbul University Hospital, authorities say.
Thursday's deadly explosion came on the same day as a smaller blast in Ankara, and four days before world leaders meet in Istanbul for a NATO summit.
Police in Istanbul said the 20-year-old female bomber, who was among the dead, was transporting the percussion bomb to another target when it exploded, according to CNN Turk reporter Serhat Ucak.
Authorities said they were casting a wide net in the city, looking for suspects. No group claimed responsibility for the blast.
Previously, police had said they were searching for an 18-year-old man, wearing jeans, who witnesses said got off the bus before the bomb exploded.
Reports on the number of wounded varied from 12 to 21.
The blast blew out the bus' windows and damaged the front and side of the vehicle, part of which was peeled back.
The hospital is in the Fatih District of Istanbul, Turkey's largest city.
The neighborhood near downtown is one of the city's busiest, with lots of shops and commercial and shopping areas.
Earlier, in the Turkish capital of Ankara, a smaller bomb blast in front of the Hilton Hotel wounded two people, including a police officer.
Police on the scene said one officer kicked the suspicious package, causing it to detonate and injure his legs.
World leaders, including President George W. Bush, will be arriving in Istanbul this weekend to attend the NATO summit Monday and Tuesday, and security has been beefed up across the country. (Full story)
Bush was to stay at the Hilton in Ankara before leaving for Istanbul. The White House said his schedule will not be changed despite the blast.
It will be the first summit for heads of state and government since NATO's enlargement to 26 members.
Turkish Foreign Minister Abdullah Gul said there also are no plans to change the summit schedule or the arrangements for talks between Bush and Turkish leaders.
"Turkey is a sufficiently strong and secure country. Such incidents happen everywhere, in London, in Paris, everywhere," Gul told reporters in Ankara.
Turkey has assigned 25,000 security forces to be on guard during the summit, which will be attended by about 45 world leaders. At least 200 streets will be closed off.
Security concerns were raised in November when more than 60 people died in bomb attacks in Istanbul.
Turkish authorities have linked the attacks -- which damaged an HSBC office, two synagogues and the British consulate -- to a terrorist group with ties to al Qaeda.
Shortly after the attacks, the U.S. and British governments warned their citizens to defer non-essential travel to Turkey for fear of further blasts. (Full story)
On Tuesday, a small bomb attached to an anti-NATO banner injured a policeman in Istanbul.
Last month, on the eve of a visit to Turkey by British Prime Minister Tony Blair, four small explosions went off in Ankara and Istanbul, targeting offices of a British-owned bank, HSBC. No injuries or casualties were reported.
In early May, Turkish authorities announced they had arrested a group of terrorists who hoped to set off explosions during the summit.
CNN's Alphonso Van Marsh contributed to this report