By Angus McDowall , Orhan Coskun and Phil Stewart
BEIRUT/ANKARA/WASHINGTON (Reuters) - The United States welcomed an apparent pause in fighting between Turkish-backed forces and Kurdish militia fighters in Syria on Tuesday, both of them members of the coalition fighting Islamic State, but it was far from clear that any truce would hold.
Washington has been alarmed by NATO ally Turkey's incursion into northern Syria, launched almost a week ago. The operation, dubbed "Euphrates Shield," aims to push back Islamic State but also to prevent U.S.-backed Kurdish militia fighters from seizing more territory along the Turkish border.
Ankara fears advances by Kurdish fighters as Islamic State is pushed out are aimed at establishing a Kurdish enclave along Syria's northern border, a move which could embolden a three-decade-long Kurdish insurgency on Turkish soil.
The Turkish incursion has left Washington scrambling to get its feuding allies to focus their firepower on Islamic State instead of each other after clashes that have threatened to unravel America's war strategy in Syria.
"The United States welcomes the overnight calm between the Turkish military and other counter-ISIL forces in Syria," White House spokesman Josh Earnest said, using an acronym for the militant group.
U.S. State Department spokesman John Kirby said the period of calm had lasted 12 to 18 hours and the United States would like it to continue so that all members of the coalition could focus their efforts on fighting Islamic State militants.
A Kurdish military official said a ceasefire between Turkey and Kurdish-backed militia fighters was holding. But Turkish military sources denied there was any such agreement, while a Turkish-backed Syrian rebel commander characterized it only as a "pause" and said that military operations would soon resume.
Turkish-backed forces began their offensive last week by capturing the Syrian frontier town of Jarablus from Islamic State; they then advanced on areas controlled by Kurdish-aligned militias which have U.S. support in battling jihadists.
Washington said the offensive risked undermining the fight against Islamic State.
French President Francois Hollande said he understood Turkey's need to defend itself but that targeting Kurdish forces battling jihadists could further inflame the five-year-old Syrian conflict.
"Those multiple, contradictory interventions carry risks of a general flare-up," he told a meeting of French ambassadors.
Ankara says it will not take orders from anyone on how to protect the nation. The Turkish foreign ministry said on Tuesday military operations in Syria would continue until all threats to Turkish security were removed and that U.S. comments on Turkey's targets in the operation were "unacceptable".
"The statements of U.S. officials about the content and the targets of the Euphrates Shield operation ... are unacceptable and are not in line with the alliance between the two countries," a foreign ministry spokesman said, adding that a complaint had been lodged with the U.S. ambassador to Turkey.
Eager to avoid more clashes between Turkey and U.S.-backed Syrian fighters, the Pentagon said the U.S.-led coalition against Islamic State was establishing communications channels to better coordinate in a "crowded battlespace".
"The improved coordination of armed activities in northern Syria will seek to assure the safety of all forces," Pentagon spokesman Matthew Allen said.
Sharfan Darwish, a spokesman for the Manbij Military Council, said a ceasefire between Turkey and the Jarablus Military Council was holding.
Both councils are allied with the Syrian Democratic Forces (SDF), a U.S.-backed alliance of groups including the powerful Kurdish YPG militia that is fighting Islamic State insurgents and has expanded along Syria's frontier with Turkey.
The Jarablus Military Council subsequently said the temporary ceasefire was "under the oversight of the international coalition led by the United States".
Two senior Turkish military sources denied any such truce had been agreed. A commander in one of the Turkish-backed Syrian rebel groups that have clashed with SDF-allied groups south of Jarablus also denied such a deal.
"There is no truce and no ceasefire. But there has been a pause for some time," the commander, who declined to be identified, told Reuters by telephone, adding that the operation would resume shortly.
A U.S. official, speaking on condition of anonymity, also declined to describe the pause in fighting as a ceasefire as such, though he said the intent was similar.
In a boost elsewhere to the fight against Islamic State, its Amaq News Agency reported that the group's spokesman Abu Muhammad al-Adnani, one of its longest-serving and most prominent leaders, had been killed in Aleppo.
AFTER COUP, MARK OF TURKISH PRIDE
Turkey's army chief earlier signaled no let-up in Ankara's Syria offensive, saying its successes showed a failed coup in Turkey last month had done nothing to dent the military's power.
"By pursuing the Euphrates Shield operation, which is crucial for our national security and for our neighbors' security, the Turkish Armed Forces are showing they have lost none of their strength," Chief of General Staff Hulusi Akar said in a statement to mark a national holiday.
Turkey is still reeling from an attempted coup in July in which rogue military commanders used warplanes and tanks to try to oust President Tayyip Erdogan and the government, exposing splits in the ranks of NATO's second-biggest military.
In a purge of suspected coup sympathizers, 80,000 people have been removed from both civilian and military duties, including many generals, officers and rank-and-file soldiers.
In its Syria offensive, Turkish forces and their rebel allies have taken a string of villages in areas controlled by the Syrian Democratic Forces (SDF) and advanced toward Manbij, a city the SDF seized from Islamic State this month in a U.S.-backed campaign.
Turkey says its forces have struck multiple positions held by the Kurdish YPG militia, part of the SDF coalition.
The YPG says its forces withdrew from the region before the Turkish assault and have already crossed the Euphrates, in line with a demand from the United States to withdraw to the eastern side of the river that flows through Syria or lose U.S. support.
Turkey wants to stop Kurdish forces taking control of territory that lies between cantons to the east and west that they already hold, and so creating an unbroken Kurdish- controlled corridor on Turkey's southern border.
(Additional reporting by Asli Kandemir, Edmund Blair and David Dolan in Istanbul, Andrew Callus and John Irish in Paris, Tom Perry, Lisa Barrington in Beirut, and David Alexander, Phil Stewart and Idrees Ali in Washington; Writing by Nick Tattersall; Editing by Ralph Boulton and James Dalgleish)