US Vice President Joe Biden on Saturday met Turkish President Recep Tayyip Erdogan in Istanbul in a bid to ease strains over the Syria crisis and persuade Turkey to step up its support for the coalition against Islamic State (IS) jihadists.
The trip to Istanbul by Biden, the highest ranking US official to visit Turkey since Erdogan was elected president after over a decade as prime minister, came amid unusual tensions in the traditionally strong relationship between the two NATO allies.
The pair did not announce any breakthrough after some four hours of talks at an Ottoman palace on the Bosphorus Istanbul. But Biden insisted that the relationship was "as strong as ever it has been".
Biden described the talks as "candid" while Erdogan said the two sides had held "detailed" discussions about the threat posed by IS.
Washington has been frustrated by the relatively limited role played by Turkey in the fight against IS fighters who have seized swathes of Iraq and Syria right up to the Turkish border.
Turkey in turn is upset that its contribution in hosting 1.6 million refugees from the Syrian conflict has gone relatively unrecognised and is wary of supporting the Kurdish fighters battling IS.
"On Syria we discussed the full range of issues and the options available to deal with those issues," Biden said after the talks.
He said this included "strengthening the Syrian opposition" and seeing a "transition" from the regime of President Bashar al-Assad.
Biden had personally stung Erdogan last month by suggesting his policies in supporting Islamist rebel forces in Syria had helped encourage the rise of the IS militant group, a slight that prompted Erdogan to warn his relationship with the US number two could be "history".
But the straight-talking Biden emphasised that openness was a key part of the US-Turkey relationship.
"We have always had direct and frank discussions on every issue, that is what friends do," he said.
Erdogan echoed Biden's praise of relations. "We want to continue our cooperation with the United States by strengthening it," he said.
Biden's office also announced that the United States would provide an additional $135 million for humanitarian aid for Syria, some of which would go to refugees living in Turkey.
"Turkey is carrying a heavy humanitarian burden," Biden said.
Signup to our newsletter and follow us on Facebook and Twitter!
- 'More in common' -
So far, Turkey's sole contribution to the anti-IS coalition has been allowing a contingent of Iraqi Kurdish peshmerga fighters to transit Turkish soil to fight IS militants for control of the Syrian border town of Kobane.
Ankara has also so far refused to allow US forces to stage bombing raids from the Incirlik air base in southern Turkey, forcing them to make far longer sorties from the Gulf.
Turkey has set several conditions for playing a greater role in the coalition.
It wants a clear coordinated strategy to overthrow Assad, a major training and equipping programme for the anti-regime Free Syrian Army (FSA), and a security zone, backed by a no-fly area, to be set up in northern Syria along the Turkish border.
US officials after the talks played down the lack of any major agreement, saying the discussion with Turkey had evolved and is now "quite dynamic".
A senior official said the two sides now have much greater clarity over their positions than was the case a few months ago. "We are convinced we have a lot more in common than disagreements."
Both sides were in complete agreement about the need to defeat IS and on the need for a political transition away from Assad, the official added.
Biden said that he discussed with Erdogan a plan to train and equip FSA fighters. This is expected to be a key part of defeating IS on the ground in Syria.
However the official emphasised that the current campaign was focused against IS, rather than the regime of Assad.
Russian Foreign Minister Sergei Lavrov on Saturday said the US-led operation against IS jihadists in Syria could be a guise for trying to "surreptitiously" topple the Assad regime.
"Possibly... this is not so much an operation against Islamic State as the preparation for an operation to change the regime surreptitiously under the cover of this anti-terrorist operation," Lavrov told a forum of politics experts in Moscow.