Qatar, which mediated the release of a US hostage held by Al-Qaeda in Syria, seeks to prove its role in confronting the Islamist radicals it has been accused of supporting, experts say.

The Qatari foreign ministry, in a statement, said the tiny gas-rich nation had "succeeded in releasing American journalist Peter Theo Curtis," after he spent 22 months in captivity.

Doha "exerted relentless efforts" to obtain the release of the freelance journalist held by Al-Nusra Front in Syria "out of Qatar's belief in the principles of humanity and its keenness on the lives of individuals and their right to freedom and dignity," it said.

Curtis's mother said the family was "repeatedly told by representatives of the Qatari government that they were mediating for Theo's release on a humanitarian basis without the payment of money."

And US Secretary of State John Kerry "thanked" the emirate for "the effort made to secure the release" of Curtis in a telephone call to Qatari Foreign Minister Khalid al-Attiyah, the official QNA news agency reported.

It was not the first time that Doha has played the role of regional mediator between the West and Islamist groups.

In June, Qatar brokered a deal under which five Taliban militants were freed in return for the release of US Sergeant Bowe Bergdahl, who was captured by Afghan militants.

Since Islamic State (IS) jihadists in Syria sparked worldwide horror last week when they released a video showing their beheading of American journalist James Foley in retaliation for US air raids against them in northern Iraq, Qatar has stepped up efforts to distance itself from radical Islam.

- Qatar 'repelled' -

"Qatar does not support extremist groups, including the Islamic State, in any way," Attiyah said on Saturday.

"We are repelled by their views, their violent methods and their ambitions," he said. "The vision of extremist groups for the region is one that we have not, nor will ever, support in any way."

Since the rise of Qatar in the regional and international political arena in the late 1990s, the energy-rich US ally has been regularly accused of supporting or financing insurgent movements, directly or indirectly, particularly in Syria.

On Wednesday, Germany's development aid minister, Gerd Mueller, accused Qatar of financing IS.

"Who is financing these troops? Hint: Qatar," he said in an interview with public broadcaster ZDF.

Germany later said it "regretted" any offence caused to Qatar by the minister's remarks.

On the diplomatic scene, Qatar's emir last week hosted talks between Palestinian president Mahmud Abbas and the Doha-based Khaled Meshaal -- head of the Islamist movement Hamas which is on a US terror list -- in a bid to resolve the Gaza conflict.

And despite unprecedented tensions between Qatar on one hand, and Saudi Arabia, the Emirates and Egypt on the other, Attiyah took part with his three counterparts in an Arab meeting held on Sunday.

The foreign ministers discussed the Syrian conflict and "challenges including the rise of terrorist extremist ideology," according to an official statement issued after the meeting in Saudi Arabia.

They agreed on "the need to seriously work to deal with these crises and challenges to preserve security and stability in Arab countries," it said.

According to experts, Qatar has been left with no choice but to join international and regional efforts to contain the rise of Islamist extremists.

The IS group is "a threat to everybody, including the Gulf countries and Qatar," said Abdulhakim Abdulla, political science professor at Emirates University.

The Qataris "don't want to upset everybody... They have to do their best to cooperate and coordinate with Riyadh," the Gulf specialist said.

Qatar's support for the Muslim Brotherhood, banned in several Arab countries and listed as a "terrorist" group by Riyadh, has already left Doha in hot water with most of its Gulf neighbours.

Saudi Arabia's grand mufti, Sheikh Abdul Aziz al-Sheikh, last week went so far as to condemn IS as the "enemy number one" of Islam.

Frederic Wehr ey of the Carnegie Endowment for International Peace agreed that Qatar is now "apparently falling into line" against IS.