Thousands of ethnic Hmong paid their last respects Friday to Laotian general Vang Pao, who led a CIA-backed "secret army" in the Vietnam war, at the start of a six-day funeral service.

But the gathering was clouded with anger when it was announced that US authorities have refused a request for the 81-year-old Hmong veteran to be buried with full honors at Arlington National Cemetery.

Military veterans who fought alongside him joined family and community mourners at the traditional funeral service in Fresno, California, where he died last month.

Shortly after the initial two-hour funeral ceremony, however, a confidant of Vang Pao said US authorities had told him they were refusing a burial at Arlington, where top US military brass are laid to rest.

"They called a little while ago... and they told me the committee turned the general down," said Charlie Waters, an American military veteran and confidant of Vang Pao told AFP, adding: "So we're appealing to the White House."

"They gave me this lame excuse that it would take it the place away from an American serviceman. That's crap," he said adding that he would offer to surrender his own place at Arlington.

Vang Pao led the Central Intelligence Agency (CIA)-backed force that assisted the United States in Vietnam, during its ill-fated war with communist forces in the north of southeast Asian nation.

He died of pneumonia on January 6 in the central California city of Fresno, one of the major hubs of the United States' 250,000-strong Hmong community, some 30-40,000 of whom live in the western US state.

Draped in the Stars and Stripes flag, Vang Pao's coffin was borne into Fresno's convention center where tens of thousands of Hmong from the United States and abroad were expected to gather over the weekend.

Rows of black-clad mourners joined ranks of soldiers in uniforms and khakis, as well as bagpipers in kilts who had accompanied the casket into the hall, to the strains of Dvorak's "New World" Symphony.

"Today our Laotian nation has lost... one of its outstanding sons," said Khamphay Abbay, a former Royal Lao official and Laotian currently living in Australia, who was an advisor to Vang Pao during the war.

California US congressman Jim Costa has led a group of lawmakers in Washington lobbying for Vang Pao to be buried at Arlington, outside Washington DC.

William Dietzel, another US friend of the Hmong general, also paid tribute to Vang Pao's support for the United States in one of its darkest hours.

"General Vang Pao will forever be remembered for his extraordinary service in the defense of freedom," he told the ceremony.

Waters, who spoke during the two-hour ceremony, lashed the Arlington decision.

"How many times can these bureaucrats hurt these people?" he said, adding: "The timing sucks .. How dare they? These people are hurting. These jerks, they could have told us a long time ago."

There was no immediate word from the Pentagon in Washington.

The central California city of Fresno is one of the major hubs of the United States' 250,000-strong Hmong community, some 30-40,000 of whom live in the western US state.

Vang Pao, a fierce opponent of the communist government in Vientiane, was also a controversial figure.

In 2007, he was arrested in California on charges of plotting to overthrow a foreign government after an undercover agent tried to sell him weapons at a Thai restaurant.

Prosecutors dropped their charges in 2009. On Monday, a judge ended the case for the remaining 11 Hmong Americans accused in the case amid persistent questions over the government's evidence.