Russia has lifted its objections to a U.N. investigation into chemical attacks in Syria, clearing the way for the probe to begin, diplomats said Thursday.

The U.N. Security Council unanimously adopted a resolution August 7 approving a joint investigation by the United Nations and the Organization for the Prohibition of Chemical Weapons.

President Barack Obama has ordered his team to admit at least 10,000 Syrian refugees next year, the White House said Thursday, amid criticism that the United States has not done enough. 

Spokesman Josh Earnest said Obama had asked staff to "scale up" the number of refugee admissions from around 1,500 in this fiscal year, to 10,000 in the next, beginning October 1.

More than 50 U.S. intelligence analysts have complained that senior military officials altered reports so as to downplay the strength of Islamic State and al-Qaida's branch in Syria, the Daily Beast reported Thursday.

The online news outlet said senior officials at U.S. Central Command changed the reports to bring them into line with the White House's rosier public view that the United States was winning the war against the militant groups.

A defiant Russia on Thursday said it was ready to increase military support to Syria's Bashar Assad if needed, dismissing suggestions it could hamper Western efforts to fight Islamic State militants.

Washington has accused Moscow of solidifying its foothold in Syria, raising concerns it could throw a wrench in plans by the U.S.-led coalition to step up operations against jihadists in the war-torn country. 

Progressive Socialist Party chief MP Walid Jumblat sought on Thursday to limit any possible tension that could emerge over the killing of Sheikh Wahid al-Balous, a prominent Druze cleric in Syria.

“This is not an opportunity to challenge anyone. We respect all viewpoints,” said Jumblat at the memorial service of al-Balous held at the Druze Community House in Beirut's Verdun district.

Militants led by Al-Nusra Front in Syria killed at least 56 soldiers, some execution-style, when they overran the regime's last base in Idlib province under the cover of a sandstorm, a monitor said Thursday.

Dozens of others were either taken prisoner or went missing when the Al-Nusra Front and a coalition of mostly Islamist groups captured the Abu Duhur military airport on Wednesday, the Syrian Observatory for Human Rights said.

Jihadists of the Islamic State group edged closer to a strategic airbase in eastern Syria in heavy clashes that left 54 fighters dead, a monitoring group said Thursday.

The extremist group, which has captured territory across Iraq and Syria, seized control late Wednesday of an army post near the regime-held military airbase outside Deir Ezzor, the Syrian Observatory for Human Rights said. 

A Turkish soldier deployed on the border with Syria was killed early on Thursday by fire from Syrian territory, the Dogan news agency reported.

The soldier, 21, was standing guard in the Reyhanli district of the Hatay region of southern Turkey when he was hit by fire from the Syrian side of the border.

Photos allegedly showing Russian soldiers, reports of military deliveries and overflight requests are swelling fears among the United States and its allies that Russia is covertly bolstering the Syrian regime.

Moscow, an ally of Syria's President Bashar al-Assad, has had a military presence in the country since the Soviet era.

The influx of refugees to Europe was triggered in part by donors taking the "cheap option" and not giving enough aid to displaced Syrians in Lebanon and Jordan, the head of the U.N. refugee agency in Jordan said on Wednesday.

Harper told The Associated Press in an interview that refugees feel betrayed by the international community and the aid agencies. This, he said, "is a reason why we are seeing movement back into Syria, and in many cases, movements continue on into Europe and further afield."