Twin blasts in Istanbul •Carbombs set off by • Attacks come as US President Bush is in London to meet British PM Tony Blair. Only 5 days after suicide bombers carried out a twin attack on Istanbul synagogues, killing 25. Pak fingerprint • DNA tests say two Turkish nationals bombed synagogues. • Turkish Daily News said police found pieces of a Pakistani passport believed to belong to one. Suspected Islamist suicide car bombers killed at least 27 people and wounded hundreds in Istanbul on Thursday in a strike against Britain that US and British leaders called a challenge to their war on terror. The Consulate’s chaplain said Consul-General Roger Short, a career diplomat, was among the 15 killed at the mission where a van pulled up on a busy street and exploded, leaving a huge crater. ‘‘We knew it was a bomb when an arm came flying through the window,’’ said a doctor at a clinic near HSBC.