Bob Sinkinson: Reports that authorities knew of planned attack on British target

As officers from London's anti-terrorist branch and the American FBI begin investigations in Yemen, reports in the British press say the Yemeni authorities were aware of a plot targeting UK tourists days before the kidnapping.

The reports say the deaths could have been avoided if UK diplomats had been made aware of the threat.

The three Britons and one Australian who died were in a party of 16 tourists ambushed as they travelled in convoy through southern Yemen.

They were killed in a gun battle in the southern province of Abyan when the Yemeni army attempted to rescue them.

The UK Government has twice summoned the Yemeni ambassador to London meetings at the Foreign Office to press for a full, detailed account of the kidnapping and rescue operation.

Foreign Office Minister Joyce Quin says Britain is "seriously concerned" at the way the hostage crisis was handled.

One of the main worries for the UK is discrepancies between accounts given by some hostages and the official Yemeni version of events.

Some of the hostages say their rescuers were firing indiscriminately as their captors used them as human shields.

But hostages arriving in Britain on Friday denied they were put under pressure to change their accounts of the shoot-out to fit in with the official Yemen line.

Islamic Jihad

Yemen says the kidnappers are part of a group calling itself Islamic Jihad and were already shooting hostages when the order was given to start the rescue.

They say the group has links to other extremist groups outside Yemen.

Osama bin Laden: Wanted by US

The Officers from the US and UK who travelled to Yemen are trying to determine whether the group is connected to the Saudi dissident, Osama bin Laden.

The US has accused him of being the mastermind behind the bombings of their embassies in Tanzania and Kenya.

The police officers will also visit the scene of the shootings and meet with senior Yemen security agents.

The BBC's Frank Gardner: "Quiet and solemn ceremony"

The bodies of the four dead hostages are being flown back to Britain.