DOHA — Qatar is working to help free four Americans held hostage in Syria by various armed groups, a Gulf source familiar with the matter said on Monday, a day after the Gulf Arab state's diplomacy helped free a journalist held since 2012. The source declined to name the four or provide details, and Reuters could not independently verify the assertion, but his account was broadly supported by other sources. The reported initiative by Qatar coincides with an effort by the tiny state to rebut accusations by some of its Arab neighbors and Western politicians that it supports the most anti-Western militant armed groups in Iraq and Syria. Those allegations followed months of criticism by human rights groups over its treatment of Asian guest workers and charges — denied by Doha — of corruption in its successful bid to host the 2022 World Cup. Qatar, which does back some rebel factions fighting to oust Syrian President Bashar Al-Assad, has mediated the release of foreign and Syrian captives on several occasions in the course of Syria's three-year-old civil war. Its latest foray into hostage diplomacy brought Sunday's release of Peter Theo Curtis, an American held for nearly two years by Al-Nusra Front, an affiliate of Al-Qaeda. "Four other Americans who have gone missing in Syria have now been located, and Qatar is working to free them," the Gulf source told Reuters on condition of anonymity. He said the hostages were being held by "various groups" but declined to give details. Qatar's foreign ministry declined to comment. A Doha-based source close to the Qatari government said without elaborating that Washington was working with Qatar to try to free a number of US hostages in Syria. A rebel commander in Syria reached by Skype from Beirut told Reuters that Qatar was continuously trying to secure the release of captives of all nationalities. "Qatar has good connection here on the ground with various groups," he said. "Freeing hostages is their priority, and whenever there is a chance, they help. They use these connections to release hostages. Right now they are working on several issues regarding hostages." A Syrian opposition official in Doha said Qatar was trying to secure the release of a number of hostages across Syria, but did not say how many. "Qatar has very good connections with brigades inside Syria. That's why their attempts have been successful, and more efforts are being made to free a number of hostages across the country," said the official, who asked not to be identified. In Washington, a US State Department spokesperson said the US government over the past two years had reached out to over two dozen countries asking for help from anyone who could help secure the release of American citizens held in Syria. News of Curtis's release emerged just days after Islamic State, a splinter Al-Qaeda group that operates in Syria and Iraq, posted a video on the Internet showing one of its fighters beheading American journalist James Foley, who was kidnapped in Syria in 2012. — Reuters