US tracked down target after following his deputy

Abu Musab al-Zarqawi, the insurgent leader blamed for the slaughter of thousands in Iraq, was killed by two 500lb bombs dropped by a US fighter jet after he was tracked down to an isolated house in a date-palm grove north of Baghdad.

General George W Casey, the top American military commander in Iraq, said the air strike at 6.15 pm on Wednesday hit "a single dwelling in a wooded area surrounded by very dense palm forest".

US and Iraqi intelligence officials discovered Zarqawi's hideout after following his deputy Abu Abdul-Rahman to a meeting in a house near the city of Baquba, 40 miles north of Bahdad. It was the final act in what the US military described as a "painstaking" spying operation involving sources within Zarqawi's network of associates.

"This gentleman was key to our success in finding Zarqawi," said Maj-Gen William Caldwell. "He was a top lieutenant ... and was identified several weeks ago. We were able to start tracking him, monitoring his movements ... Last night, he went to meet [him] again at 6.15pm [2.15pm GMT] when the decision was made to go ahead and strike that target."

Maj-Gen Caldwell added: "What everyone needs to understand is the strike last night did not occur in a 24-hour period. It truly was a very long, painstaking, deliberate exploitation of intelligence, information gathering, human sources, electronics, signal intelligence that was done over ... many weeks."

Two US Air Force F-16 fighter pilots flying a previously scheduled mission at "medium altitude" were given the target and orders to attack it, explained Lt-Gen Gary North, the senior air commander in the region. "We had 100 per cent assurance that Zarqawi was in the safe house," he said. The explosion of the laser-guided bombs killed Zarqawi and seven of his lieutenants. His body was later identified by fingerprint evidence and from known scars on his corpse. A statement from al-Qa'ida in Iraq, the movement he led, later confirmed he had been killed. The organisation's members vowed to continue the "holy war", saying: "We want to give you the joyous news of the martyrdom of the Mujahed Sheikh Abu Musab al-Zarqawi."

The US military showed a video of the strike that killed him, alongside two photographs of his body: Zarqawi's eyes shut; his nostrils filled with blood; with gashes to his forehead and cheek. The body of Abdul-Rahman was also identified.

President Bush said Zarqawi's death was "a severe blow to al-Qa'ida and it is a significant victory for the war on terror". But he added: "We have tough days ahead of us in Iraq."

In London, Tony Blair avoided triumphalism. Zarqawi's death was "very good news because a blow against al-Qa'ida in Iraq was a blow against al-Qa'ida everywhere," he said.

But he warned that there would be reprisals - and indeed there were. At least 31 people were killed in a spate of bomb attacks across Iraq yesterday. The deadliest blast saw a roadside bomb kill 13 people in a crowded market in the east of the country.

The death of Zarqawi is a boost to the new government of Nouri al-Maliki, which was able to appoint defence and interior ministers yesterday after months of wrangling. But the US government and US army, both of which have been battered by criticism, also wanted a share in the success. Mr Maliki had to share the podium at his press conference in Baghdad with General Casey.