|Marchant was attempting to visit a dissident Catholic priest when he was stopped by police
The US has registered a protest with the Vietnamese government after it said one of its diplomats was manhandelled and detained by police in central Vietnam.
Radio Free Asia, which is funded by Washington, reported on Thursday that the diplomat was trying to visit the home of a Vietnamese dissident in the city of Hue when police stopped him.
Christian Marchant, a political officer at the US embassy in the capital Hanoi, continued to try to reach Thadeus Nguyen Van Ly, with whom he had an appointment, and was reportedly then wrestled to the ground and driven away in a police car.
"It's a clear violation of the Vienna Convention" which governs the protection of diplomats, a US official, who declined to be named, said. "We're quite concerned by it."
Ly, a dissident Catholic priest, was sentenced to eight years in prison in 2007 on charges of trying to undermine the Communist government.
The sixty-seven-year old was released for a period of 12 months last year after suffering a brain tumour and is now under house arrest.
His temporary release expires in March 2011.
The US embassy in Hanoi confirmed only that the diplomat had been manhandelled.
"We are aware of and deeply concerned by the incident in Hue and have officially registered a strong protest with the Vietnamese government in Hanoi as well as the Vietnamese Embassy in Washington, DC," Beau Miller, an embassy spokesman, told Al Jazeera.
"Diplomats are entitled under international law to special protection against attack and the government of Vietnam has responsibility to take appropriate steps to prevent any attack on the person the freedom or the dignity of the diplomat."
Police in Hue did not comment on the incident.
The US has pushed Vietnam for an improvement in its human rights record in the past.
Washington has called for the government to allow people of all religions to practice their faiths freely and to stop jailing pro-democracy dissidents.
Vietnam does not permit any challenge to its one-party rule.