Four hostages dramatically escaped early Wednesday from a hijacked Afghan jet grounded at an airport near London, amid mounting speculation of an asylum motive for the hijack now entering its fourth day.

Police said none of the escaped men was a hostage-taker, but could not say whether they were passengers or members of the Boeing 727's crew. They said they had been in touch with the hijackers immediately afterwards and were assured that the atmosphere on board remained calm.

"The mood on board is still calm, the negotiations continue, and that is a good sign," Assistant Chief Constable Joe Edwards told a news conference at Stansted early Wednesday. However, he conceded that the "spontaneous escape" has "obviously changed the dynamic of that negotiation. That is a sensitive area."

Three of the men were spotted by television cameras as they jumped from a cockpit window before running across the apron of Stansted airport, around 80 kilometers (50 miles) north of London. Police later said a fourth man had also jumped and escaped. "The men ran towards the police containment area, where they were met and taken to a safe area for an immediate health check," Edwards said. "We do not believe they were hostage-takers... It was spontaneous. We had very little notice." He said the four men appeared to be in good health and were taken away for debriefing.

The development came suddenly as the more than 150 hostages and hijackers appeared to be settling in for a third night on the tarmac. Taking the escapees into account, the number of people remaining on board, including the hijackers, was put at 152, made up of 114 men, 17 women and 21 children. So far the only clear demands from the hijackers have been for food, water and medicines, and the motive for the hijacking remains unclear.

Interviews with hostages released from the plane in the past two days had shown there were between six and 10 armed hijackers on board, Edwards told an earlier press briefing. The hijackers had released a hostage earlier Tuesday, a man in his forties who was suffering from asthma, bringing to nine the number released, not counting Wednesday's escapees since the plane arrived at Stansted early Monday.

The Ariana airlines jet was seized during a domestic flight in Afghanistan early Sunday. Twenty-three passengers were freed during stops in Central Asia and Russia en route to London.

Earlier, a London-based representative of the UN refugee agency arrived at Stansted. Edwards refused to elaborate on what led to the UNHCR presence, nor if it had followed any plea for asylum, saying the subject was "sensitive." "There is nothing particularly significant in this move. The main strength the UN representative will bring is an intimate knowledge of the situation in Afghanistan," he said. "She will play no part in the negotiation, but will be on hand to provide background information and advice." Nevertheless, speculation was beginning to focus on a theory that the motive for the hijack was to seek asylum in Britain. Officially, police are not commenting. They say the hijackers have made no political demands, although "certain other issues have been discussed." The Daily Mail said three hostages freed earlier from the jet had already requested political asylum, and that some of the hijackers may have relatives on board. According to the Daily Telegraph citing police sources, the hijackers have asked negotiators what would happen if they surrendered. The Times, for its part, said the negotiations were concentrating on the hijackers' demands for assurances about their personal safety, and that they had been promised they would not be returned to Kabul. It quoted an unidentified police source as saying they were "men who want to save their own skins and not Islamic zealots pursuing a holy cause". The hardline Muslim Taliban regime in Kabul had accused warlord Ahmad Shah Masood of orchestrating the hijacking to win the release of jailed opposition leader Ismail Khan. Masood's brother Wali Masood denied the allegations.

Afghanistan is one of the top sources of asylum seekers coming to Britain, with refugee status being granted in about a third of cases.

An average of 360 asylum applications a month have been lodged by Afghans since October.