Turkish police are investigating the possibility that one of the four gunmen who attacked the US consulate in Istanbul had links to al-Qaeda.
Three policemen and three of the attackers were killed during a gun battle in the city on Wednesday.
A Turkish government official said one of the attackers was known to have travelled to Afghanistan, AP reports.
Meanwhile, police may have captured the fourth gunman and seized a car used in the attack, according to local reports.
Private news agency Dogan and CNN Turk said the man was being questioned by police.
The suspect is believed to have fled the scene after driving his fellow attackers there.
Four other suspects were detained on Thursday as police investigated their possible ties to the attackers, Interior Minister Besir Atalay told reporters.
Earlier, the funerals of the three policemen killed in the attack took place in Istanbul.
Mr Atalay paid his respects to the dead officers, one of whom had only been in the police force for two weeks.
He went on: "Our fight against terror will continue. Those who support and feed terror should know that terror will destroy them."
The motive for the attack is still being investigated, the BBC's Sarah Rainsford in Istanbul says, and there has been no official statement on media reports quoting police sources linking the attackers with al-Qaeda.
The relatively amateur nature of the shooting has led some to doubt whether it is the work of al-Qaeda, she adds.
Witnesses
A US state department spokesman said he could not confirm or deny reports of al-Qaeda involvement in Wednesday's attack.
According to witnesses, three men emerged from a car just outside the US consulate building, surprising police officers and opening fire.
Turkish newspaper Milliyet reports that one of the attackers - named as 26-year-old Erkan Kargin - travelled to Afghanistan two years ago where he was trained.
On Wednesday, Turkey's interior minister confirmed that one of those who took part in the attack had previously travelled abroad.
The two other gunmen killed in the assault are named as Bulent Cinar and Raif Topcil. Both are reported as having convictions for minor offences.
Armed groups
A police official is quoted as saying that if the al-Qaeda link was proved, it would be the first time that members of the group had used firearms in such an attack.
On Wednesday, reports quoted police sources as saying the suspects belonged to a Turkish Sunni Islamic fundamentalist group called the Great Eastern Islamic Raiders Front, thought to have links to al-Qaeda.
Turkey has seen armed attacks from a variety of groups in recent years.
The most deadly was in November 2003, when 58 people were killed by Islamist militants in suicide bombings outside two synagogues, the British consulate and a British bank in Istanbul.
The Kurdish rebels of the PKK have also been blamed for several attacks, including a car bombing that killed six people in the city of Diyarbakir in January.
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