China is known to take a jaundiced view of increased military ties between Vietnam and the US.

The unexpected restrictions stopped doctors from the US and seven other nations, including Singapore, from performing operations on Vietnamese citizens.

The medical mission began two weeks ago when an American warship, the USS Peleliu, arrived in Danang in central Vietnam with 1,200 crew supplemented by 300 health professionals.

While the foreign medical staff were mostly Americans, they also included doctors from Singapore, India, Malaysia, Japan, South Korea, Canada and Australia.

The warship arrived here from the Philippines, where the multi-nation medical force had provided a wide scope of services. There, US Sea Dragon helicopters had ferried Philippine patients to and from shore for 160 surgical procedures in the ship's two operating theatres.

But Vietnam forbade use of the US helicopters and refused to allow any patients to undergo operations on board the Peleliu, officers said.

A Japanese naval doctor told The Straits Times: 'No surgeries have been allowed because the Vietnamese Ministry of Health put constraints on us. It's been very frustrating.'

Other officers confirmed that they had only been allowed to provide verbal advice and exchange views with Vietnamese counterparts.

The last-minute restrictions imposed by Hanoi were principally made to avoid incurring the wrath of China.

Said Professor Carlyle Thayer, a Vietnam expert at the Australian Defence Force Academy: 'All cooperative defence activities with the United States are viewed by Vietnam through the lens of what impact they are likely to have on relations with Beijing.'

A party source familiar with the issue told The Straits Times: 'We wanted to let the American ship people do all they wanted, but we had to limit them or risk irritating Beijing.'

Despite the constraints, there were notable achievements. Around 2,300 patients received attention from the visiting medical contingent.

But it was the restrictions placed on their services that disappointed many.

Said the US Ambassador to Vietnam, Mr Michael Marine: 'I share the disappointment to a certain degree because if we had been allowed to offer the full range of services, they would have been successful. But I'm very pleased with what we have been able to do.'

ROGER MITTON