A BBC correspondent in Vietnam for US President Barack Obama's visit to the country said today he had been ordered by the Vietnamese authorities to stop reporting apparently because they suspected he had met one of the government's sharpest critics.

"We have now been told that our accreditation has been withdrawn and all our reporting activities must stop," Bangkok-based Jonathan Head said in a report on the BBC's website.

Vietnam's foreign ministry had no immediate comment.

There were no other indications of a clampdown on foreign media and local media reported at length on Obama's three-day trip, which is aimed at bolstering diplomatic, economic and military ties though the U.S. side is expected to prod Hanoi on human rights.

There was no suggestion that Head had been told to leave.

Earlier this month North Korea expelled a BBC journalist for his reporting as a large group of foreign media members visited the isolated country to cover a ruling party congress.

Communist party-ruled Vietnam has long been suspicious of the BBC, whose Vietnamese-language service is routinely blocked in the country because it often reports on human rights issues.

The BBC World's TV service is relayed with a 10-minute delay in Vietnam. An on-camera report by Head from Hanoi on Monday was blocked for about 10 seconds, with a notice on the screen saying the programme was temporarily suspended.

Head said no reason was given by the authorities for the ban on his reporting activities.

But he said that "in a fraught exchange" with officials it was suggested that it was because he had met Nguyen Quang A, one of about 20 dissidents who tried to run as independents for an election to parliament that took place on Sunday.

Head said he had not met Quang A, who was detained twice last year after meeting political prisoners and attending democracy seminars abroad, and failed to get onto the ballot for the National Assembly election.