Washington, Aug 11 (IANS): US President Joe Biden said that Washington knows "with certainty" that the Syrian government has held Austin Tice, a reporter and former Marine missing in Syria since 2012, and is asking for its help bringing him home.

Marking a decade since Tice was taken captive, Biden on Wednesday said that "there is no higher priority in my administration than the recovery and return of Americans held hostage or wrongfully detained abroad", reports dpa news agency.

Tice travelled to Syria in 2012 to cover the war as a freelance journalist for McClatchy, The Washington Post, and other publications.

US officials believe he was detained at a Syrian government checkpoint southwest of Damascus on August 14 of that year.

A video emerged six weeks after his disappearance purporting to show him in captivity.

"We know with certainty that he has been held by the Syrian regime. We have repeatedly asked the government of Syria to work with us so that we can bring Austin home. On the tenth anniversary of his abduction, I am calling on Syria to end this and help us bring him home," Biden said.

Biden administration officials have said they operate on the "sincere belief" that Tice is alive.

The Syrian government, however, has denied any knowledge of his whereabouts or condition.

Also issuing a statement, Secretary of State Antony Blinken said the US continues to "demand" that Syrian officials "acknowledge the detention of Austin and every other US national held in Syria, a responsibility under international law and an important step in securing their release".

The US special presidential envoy for hostage affairs, Roger Carstens, "will continue to engage with the Syrian government" in coordination with the White House, State Department, and law enforcement agencies, Blinken said.

In May, Biden held a meeting with Marc and Debra Tice at the White House to discuss their son's case.

The Tice family pleaded with the President to directly engage with the Syrian government of Bashar al-Assad on Tice.

Biden told the family he would direct his team to meet with the Syrians as soon as possible.

In his statement on Wednesday, Biden said the family "deserves answers, and more importantly, they deserve to be swiftly reunited with Austin".

"We stand with Austin's many loved ones, and we will not rest until we bring Austin home. Ten years is far, far too long... So is every additional day."