Just three days before the start of a Nato summit in Istanbul attended by 40 world leaders including Tony Blair and President George Bush, two bombs exploded in Ankara and Istanbul yesterday, killing at least three people and injuring 18 others, heightening security fears.
Those who died were on an Istanbul bus when a bomb exploded as the vehicle passed a hospital. Fifteen people were injured. Earlier, a small bomb exploded 75 metres away from the Ankara Hilton hotel where Mr Bush is due to stay, injuring three people.
The bomb was attached to a banner which read "Stay Away Bush!". A Marxist group claimed responsibility for that attack. "I saw smoke coming out of the bus," said Kaval, a witness in Istanbul. "I saw people jumping out of the windows. It was a horrible scene. I saw people without arms and whose feet were ripped off."
Police said that three suspects had been arrested in connection with the bus attack.
Turkey has taken extraordinary security precautions in Istanbul, fearing a repeat of four truck bombs there last November that killed more than 60 people.
Prosecutors say that a Turkish al-Qa'ida cell was responsible for those attacks on two synagogues and two British targets, including the British consulate. The Ankara government, which hosts the Nato summit in Istanbul on 28-29 June, was quick to try to play down security concerns.
"Turkey is a sufficiently strong and safe country. Such incidents happen everywhere, in London, in Paris, everywhere," Abdullah Gul, the Foreign Minister, told reporters.
A spokesman for Mr Bush said there would be no change in his travel plans despite the attacks. Bush is scheduled to arrive in Ankara late tomorrow night and to move on to Istanbul on Sunday evening.
Hundreds of Turks have taken to the streets protesting against Mr Bush's visit. So far violence has been limited to a smattering of percussion bombs, designed to create a lot of noise but not much damage. Officials expect several thousand people, including some 500 anti-globalisation protesters from abroad, to take part in rallies this weekend.
Surveillance planes will patrol above Istanbul and 30,000 officers will police the streets. The Bosphorus waterway will be closed to traffic, including oil tankers, and the subway system will be suspended. The conference zone in the heart of the city is to be sealed off with concrete barriers and all residents are required to show ID. Many companies are closed for business during the summit.
Turkish officials blamed far-left groups for yesterday's attacks. The Istanbul governor, Muammer Guler, said the bomber on the bus was a woman in her mid-twenties who was carrying the bomb in her lap when it exploded in the mainly residential Fatih district of Istanbul.
"The bus was not the target. The bomb was being carried from one place to another," Mr Guler said. "We suspect a Marxist-Leninist group."
Turkish police have been preparing for the Nato summit for months. Militant Islamic, Kurdish and leftist groups have carried out past attacks in Turkey, and hundreds of people have been detained and questioned in surveillance sweeps, including 16 alleged members of Ansar el-Islam said to be planning an attack.
Two of the alleged masterminds behind the November attacks are still at large however, and are believed to have fled the country.