A US military helicopter crashed in northeastern Afghanistan on Sunday killing two of the seven Marines on board, while in the south of the country tribal forces pressed the hunt for Taliban leader Mullah Mohammad Omar.

Afghanistan's interim leader Hamid Karzai arrived in Tokyo for an international conference on Monday and Tuesday where he must outline a vision of how to rebuild his devastated country and make his case for aid.

The world hunt for members of Osama bin Laden's al Qaeda network spread further afield with the arrest of two men in Spain.

A US Super Stallion helicopter, supplying forces in the hunt for Bin Laden and Mullah Omar, came down in rugged mountains after setting out from Bagram air base to the north of the capital, Kabul.

Captain Tom Bryant said the helicopter made a "hard landing" at around 0330 GMT about 60 km south of Bagram.

"Seven Marines were on board the aircraft, two were killed, five were injured," Bryant told reporters at Bagram, adding that the Marines have all been evacuated from the crash site to an undisclosed US facility via Bagram.

"The five injured Marines were all in stable condition, two of them were critical, two were serious and one had minimal injuries," Bryant said. Bryant said investigations were continuing but it was too early to determine the cause of the crash.

Earlier this month, a US military refuelling plane crashed in southwestern Pakistan, killing all seven Marines on board.

At least two helicopters crashed in the early stages of the war, and two Marines were killed in the first accident near a base in Pakistan.

A British passenger jet made an emergency landing in Iceland on Saturday after a message was scrawled on a toilet mirror saying a bomb was on the flight from London to Orlando, Florida. Police were searching for clues about who made the threat.

"There is a bomb America must die Bin Laden is a hero," the message read.

Bin Laden's former Afghan host, Taliban chief Mullah Omar, was moving from place to place, but was being hunted by tribal forces loyal to the interim government, the governor of southern Afghanistan's Kandahar province, Gul Agha, told Reuters.

Once found, the reclusive ruler of the austere movement that governed Afghanistan for six years would be arrested, Agha said.

"He is still in Afghanistan," Agha said. "He is moving from place to place. When we catch up with him, he will be arrested."

Karzai arrived in Tokyo from Saudi Arabia, which is co-chairing the aid conference, with a commitment that the oil-rich kingdom would seek to improve ties with his government.

Saudi diplomats say relations with the interim Afghan government have been strained over reports of killings and maltreatment of Saudi nationals suspected of being al Qaeda members captured by the anti-Taliban Northern Alliance.

The kingdom says it wants custody of any of its nationals and will punish those with links to Bin Laden, who was stripped of Saudi citizenship in 1994.

Diplomats and UN officials said security would be a top priority at the Tokyo conference for both donors and the Afghan government because without it, reconstruction would fail.

"Unless the security issue is grappled with, there isn't going to be a viable programme," said Mark Malloch Brown, who leads UN reconstruction efforts in Afghanistan.

Karzai's month-old government faces a major challenge in imposing order in a country where rival warlords still fight over tracts of land, pockets of Taliban fighters stage raids on strategic outposts and gangs loot towns and rob aid convoys. - Nampa-Reuters