U.S. President Barack Obama said on Monday that if Syria were to move or use its chemical weapons it would be a "red line" that would change his perspective on how to respond to the conflict.

Obama said he had not ordered U.S. military intervention "at this point," but warned that the United States was "monitoring the situation very carefully, and we have put together a range of contingency plans.

The end of the Muslim holy month of Ramadan gave way to an involuntary fast on Sunday in the war-torn Syrian city of Aleppo, with food and the money to buy it in increasingly short supply.

On the first day of Eid al-Fitr, the feast marking the end of Ramadan and one of the holiest days in the Islamic calendar, Aleppo's Shaar roundabout is usually packed with people shopping and visiting relatives.

Syria lashed out on Monday at comments by new international peace envoy Lakhdar Brahimi describing the increasingly brutal 17-month conflict as a civil war.

"To speak of civil war in Syria contradicts reality and is found only in the head of conspirators," the foreign ministry said in a statement published by the official SANA news agency.

U.S. Vice President Joe Biden on Monday was to meet King Abdullah II of Jordan, a key U.S. ally in the Middle East that has seen an influx of refugees from the conflict in neighboring Syria.

The two were scheduled to meet at 4:15 pm (2015 GMT) at the vice president's residence in the U.S. capital, the White House said, without providing further details.

French President Francois Hollande was due later Monday to meet with the new United Nations peace envoy to Syria, Lakhdar Brahimi, Hollande's office said.

Brahimi, a veteran diplomat troubleshooter, was named on Friday to take over from Kofi Annan after Annan quit because of the lack of international support for his peace plan.

A high-ranking Syrian military official died last week at a Russian military hospital and the body was covertly transported to Damascus, well-informed sources told the government-funded Russia Today television.

“The Syrian military figure died of serious wounds incurred during the acts of violence that have been raging there since months,” the sources told Russia Today.

Turkey cannot handle more than 100,000 Syrian refugees and instead proposes a U.N. buffer zone inside Syria to shelter them, Turkish Foreign Minister Ahmet Davutoglu said in remarks published Monday.

"If the number of refugees increases to 100,000, we will not be able to shelter them in Turkey. We have to welcome them in Syrian territory" under U.N. auspices, Davutoglu told the newspaper Hurriyet.

The Muslim Eid al-Fitr holiday got off to a bloody start in Syria, with at least 84 people dying across the country, most of them soldiers, and Damascus rocked by clashes, a watchdog said on Monday.

The fresh surge of violence on Sunday, the first day of the Eid festivities, came as new U.N. peace envoy to Syria, Lakhdar Brahimi, said it was no longer a question of "preventing civil war" in Syria but rather ending it.

Al-Meqdad clan’s spokesman Maher al-Meqdad warned that the family’s military wing could resume the kidnapping of Syrians after the Eid al-Fitr holiday if Hassan al-Meqdad was not released by Syrian rebels.

In remarks to a TV station, the spokesman said Monday: “The family took the decision to relieve people during the Eid but we will relaunch our movement after the holidays.”

The United Nation's troubled observer mission to Syria has officially ended after being recalled amid escalating violence as world powers fail to agree how to end months of bloodshed in the country.

The mandate of the U.N. Supervision Mission in Syria (UNSMIS) expired at midnight Sunday after a roughly four-month deployment in which its work was hobbled by growing unrest that has cost tens of thousands of lives.