WASHINGTON (Reuters) - A Trump administration envoy on Tuesday urged Syria’s ally Russia to push for the release of Austin Tice, an American freelance journalist kidnapped in Syria six years ago.

Robert O’Brien, U.S. President Donald Trump’s special envoy for hostage affairs, said Trump would take measures necessary to facilitate Tice’s freedom if it would help. He did not elaborate on the measures.

“We are continuing to call on the Russians to exert whatever influence they have in Syria to bring Austin home,” he said. The Syrian government says it is unaware of Tice’s whereabouts.

O’Brien came to Trump’s defense when asked why the president has made no public pronouncements on Tice but had spoken out in the cases of Americans held in Turkey, North Korea and Iran. He said Trump and his top aides are closely tracking the case.

O’Brien spoke at a news conference called to announce a National Press Club drive for private donations to match a $1 million FBI reward for information leading to Tice’s freedom.

Tice was 31 years old when he was abducted in August 2012 while reporting in Damascus on the uprising against Syrian President Bashar al-Assad.

He has not been heard from publicly since a video posted online weeks after he disappeared showed him in the custody of armed men. O’Brien said the United States believes Tice is alive but did not elaborate on the journalist’s condition.

Washington has declined to identify who it believes is holding Tice but has sought the help of Russia, Assad’s main foreign backer in the civil war, and other countries.

Tice’s father, Marc Tice, said that he and his wife will travel to Beirut later this year on at least their seventh trip to apply for visas to enter Syria to seek their son’s release.