Twenty-seven people were killed and hundreds wounded on Thursday in truck bomb attacks on the British consulate and the London-based global bank HSBC.
British Foreign Secretary Jack Straw said the attacks bore all the hallmarks of the al-Qaida network. He also confirmed the UK had warned of a possible attack in Turkey.
"Some people have been arrested but it's too early to give any information about them," said Turkish Foreign Minister Abdullah Gul at a joint news conference with Straw in Istanbul on Friday.
Turkish daily Hurriyet said on Friday seven people had been arrested over Thursday's blasts, which it said were carried out by Turkish bombers.
The strikes coincided with a visit to Britain by US President George Bush and appeared to mark a direct challenge to the two leading forces in the occupation of Iraq.
UK Foreign Secretary Jack Straw
(R) tours the scene of the attack
But British and US leaders, as well as Gul, said they would not give in to the attacks.
Asked whether there were any specific leads pointing to al-Qaida, Straw replied: "What I said was they appear to have been perpetrated by al-Qaida and its associates. More detailed information about who precisely caused this is still coming forward from the investigation."
Among the victims of the attack, which came five days after a double suicide lorry bombing against Istanbul synagogues that killed 25, was British Consul-General Roger Short.
An Istanbul police spokesman said there had been no specific warning before the bombings.
The British foreign secretary admitted the UK had issued warnings after receiving information about further attacks in Turkey, Aljazeera.net’s correspondent in Istanbul said.
But Straw praised the Turkish government and security services for their ongoing efforts to combat terrorism.
Straw, who flew to Istanbul Thursday evening, denied either London or Ankara had been lax in providing security for British interests in Turkey.
“It will always be possible for some terrorists to get through,” he said.
The US, Britain and Australia have all issued travel warnings for Turkey, saying their citizens should not visit the country unless the trips was essential. All three countries have troops stationed in Iraq.