The mother of American reporter Austin Tice, who has been missing in Syria for more than three years, believes her son is alive and called on the Syrian government to aid in his release.

Tice went missing in Damascus in 2012 and the US State Department said in March that Washington had been in periodic, direct contact with the Syrian government regarding his case, a statement his mother said provided a glimmer of hope.

"We ask both governments to work together and to work effectively to locate Austin and to secure his safe release," Debra Tice said following a news conference in Beirut on Tuesday (19 May), during a trip to mark more than 1,000 days since he disappeared.

She said the family had received information from unspecified sources about her son's condition several weeks ago.

"We hear that he is well, that he is safe, which is of course very important, and the most important thing is for us to stay patient," she added.

Tice had worked for publications including McClatchy Newspapers and The Washington Post. His family says it is unclear who is holding him.

Reporters Without Borders says 25 journalists are being held by hardline groups in Syria, five of them foreigners. It says 30, mainly Syrian journalists, are in government prisons.

"Credible sources say that Austin is alive, and not being detained by religious extremist groups. The Syrian government denies holding Austin Tice but we believe that it has the ability, it can do a lot, so that Austin Tice returns home safe and sound," Reporters Without Borders Secretary-General Christophe Deloire told a news conference.

Debra Tice said somebody must know of her son's whereabouts.

"We know Austin is not being held by any part of the opposition. Still, after all the 1009 days, we do not know where he is nor who is holding him. Someone, someone possibly near this place, knows something about my son and his whereabouts," she said.

She said a friend of the family, who is known to Shi'ite Muslim leaders in Lebanon, had offered to act as an intermediary and called on her son's captors to consider allowing that person to meet with her son.

She said the US government had not offered her family enough support and that there had been too long a delay in establishing contact with Damascus.

The United States vowed last week to 'work tirelessly' to bring him home.

"I long to hold my son in my arms," she told journalists, holding back tears. "I want my family to be whole again."

More about Syria