The highly-sophisticated bomb that went off moments after Musharraf's motorcade passed over a bridge in Rawalpindi was delayed by crucial seconds by jammers that temporarily disabled the bomb, officials said on Wednesday.

"It was enough time for Musharraf to cross the bridge," an intelligence official said. No one was hurt in the blast.

Investigators have yet to identify any suspects, but are looking into the possible involvement of al-Qaida and banned Pakistani groups.

The bomb - estimated to contain 250kg of explosive - was believed to include both a remote control and a timing device to trigger it, intelligence officials said.

The equipment in Musharraf's car jammed the timer for about a minute, and also jammed the remote control, the officials added.

The jammers usually work by emitting a magnetic impulse to block frequencies used to trigger explosive devices - including the electronic signals from precision timers.

On Tuesday, the president visited the blast site and asked investigators to find the people who were behind it as soon as possible.

"The United States strongly condemns this attack against Pakistan's president. His country is one of our closest allies in the global war on terror"

US State Department

The United States on Tuesday condemned the assassination attempt against Musharraf, a key ally in its anti-terror campaign.

"The United States strongly condemns this attack against Pakistan's president," the State Department said in a statement.

Ten suspects held

The Pakistani authorities have arrested 10 people, including Afghans, for suspected links with al-Qaida and Taliban, officials said on Wednesday.

The suspects were arrested in Rawalpindi on Monday, but the interior ministry said the arrests were not related to the assassination attempt on Musharraf.

"These arrests are not related to this incident. These are related to al-Qaida and Taliban," said Brigadier Javed Iqbal Cheema, a senior interior ministry official.

He said some weapons were recovered from the detainees, but did not say how many Afghans were among those arrested.