NEW YORK (Reuters) - NATO Secretary-General Jens Stoltenberg said on Sunday he was ready to discuss Syria with Russia and stressed the need for coordination to avoid any "incident or accident" between Russian forces and U.S.-led forces fighting Islamic State.

Speaking to Reuters on the sidelines of the U.N. General Assembly in New York, the former Norwegian prime minister said it was "too early to determine" what Russian plans were in Syria, but it had increased military presence there, including warplanes and air defenses.

"Of course there is a need to make sure that there is no incident or accident and that there are mechanisms for de-conflicting the increased military presence of Russia with the ongoing efforts of the coalition fighting ISIL, he said, using a common acronym for Islamic State.

Stoltenberg, who will meet Russian Foreign Minister Sergei Lavrov in New York on Monday, urged Russia "to play a constructive, cooperative role in fighting ISIL" and added that supporting Syrian President Bashar al-Assad "is not a constructive contribution to finding a solution."

"There is a need at least to de-conflict the presence of Russian military forces in Syria and the presence of coalition forces fighting ISIL," he said, adding that he welcomed the contacts that had taken place already between the United States and Russia.

U.S. Secretary of State John Kerry said earlier on Sunday that it was vital to coordinate all efforts against the Islamic State but this was not yet happening.

Asked about French air strikes conducted independently of the U.S.-led coalition, Stoltenberg said he welcomed "efforts by all NATO allies to fight ISIL."

Stoltenberg did not rule out an expanded role for the 28-nation North Atlantic Treaty Organization in the fight against ISIL, but declined to say what this might involve.

"I think it would be wrong of me to announce, or to speculate on any additional roles," he said. "We have to address that if and when it’s on the agenda."

Stoltenberg said it had been "encouraging" to see a ceasefire "mainly holding" in Eastern Ukraine, where Russia has been backing anti-Kiev separatists, but said he would be "very careful about speculating on any links between Ukraine and the Russian presence in Syria."

"There is still a substantial Russian military presence, both close to the borders of Ukraine and also inside Ukraine. This happens at the same time as we see a lull in the fight."

Stoltenberg said the situation in Eastern Ukraine remained "very fragile" and called on Russia to fully respect the February Minsk peace agreement by withdrawing all its support and forces.