United Nations Secretary-General Ban Ki-moon said Monday that a shaky cease-fire in Syria is holding "by and large" on its third day despite sporadic fighting and growing accusations of violations.
A war of words between the Syrian government and Saudi Arabia, a key backer of the opposition, has meanwhile added to the rising tensions.
The Syrian Foreign Ministry said recent statements by Saudi Foreign Minister Adel al-Jubeir were "lies meant to boost the morale" of militants who have suffered setbacks in Syria in recent weeks and demonstrate the kingdom's "destructive role" in Syria.
Al-Jubeir had reiterated Saudi Arabia's longstanding position that Syrian President Bashar Assad must leave power, either peacefully or through military means. The foreign minister also accused Syrian forces of violating the cease-fire.
Speaking to reporters Monday in Geneva, Ban confirmed receiving a letter from the High Negotiations Committee, the main umbrella opposition group, complaining of continuing violations by the Syrian government and its Russian and Iranian backers.
The letter sent Sunday urged the UN to help "specify the territory covered by the truce to prevent hostilities."
The Russian and US-brokered cease-fire that went into effect Saturday excludes the Islamic State group as well as Al Qaeda's branch in Syria, the Nusra Front. The cease-fire has significantly reduced violence across the war-ravaged country, bringing some respite to civilians, particularly from airstrikes.
But accusations of breaches by both sides threaten to undermine the deal, which aims to bring the Syrian government and the opposition back to peace talks in Geneva next week. Ban told reporters he wanted the cease-fire extended beyond the planned duration of two weeks.
The UN also said it plans to deliver life-saving humanitarian assistance to about 154,000 people living in besieged locations inside Syria over the next five days. A briefing note sent out by OCHA on Monday said the assistance will include food, water and sanitation supplies, as well as non-food items and medicine.
An official with the Syrian Arab Red Crescent said dozens of trucks carrying aid started entering a besieged rebel-held suburb of the Syrian capital, Damascus, for the first time since the cease-fire went into effect.
Muhannad al-Assadi told The Associated Press that the 51 trucks are carrying domestic supplies such as blankets, soap and diapers. He said it is the third aid convoy that has been allowed to enter the suburb of Moadamiyeh in recent weeks.
Aid deliveries are a main opposition demand ahead of the planned resumption of peace talks in Geneva on March 7. An attempt to restart talks collapsed earlier this month over escalating violence, including a massive Russian-backed government offensive in Aleppo.
Fighting in Aleppo province continued Monday, with Syrian state media reporting that troops and other pro-government forces have opened the road linking the northern city of Aleppo with central and western Syria after it was cut by the Islamic State group last week.
Lebanon's militant Hezbollah group said it had recovered the body of a senior commander, Ali Fayyad, who was killed during fighting in the region. The Shiite group fighting alongside Assad's forces in Syria said body of the commander, locally known as Haj Alaa, was recovered Sunday night in an operation in which Syrian and Hezbollah special forces took part.
Fayyad was a Hezbollah veteran who had led major battles against the Israeli army in south Lebanon. Lebanese media say he was among four Hezbollah fighters killed in Aleppo last week.
In the central province of Hama, warplanes carried out repeated attacks on the village of Harebnafsah amid fighting between troops and militants, according to the Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees, both opposition monitoring groups. The LCC said the warplanes were Russian. It was not immediately clear which militant groups were taking part in the fighting.
The Observatory reported that government forces captured an area near the Damascus suburb of Harasta after a day of fighting with militants, including the Nusra Front.
The opposition on Sunday reported air raids on several parts of northern Syria and warned that continued violations would jeopardize the planned resumption of UN-brokered peace talks.
Riad Hijab, who heads the Saudi-backed High Negotiations Committee, said in the statement to Ban that Russian, Iranian and government forces have not stopped hostilities since the cease-fire went into effect.
Hijab said there had been 24 instances of shelling and five of ground attacks. He added that Russian warplanes carried out 26 airstrikes on Sunday alone targeting rebels that are abiding by the truce.
The French foreign minister called for a meeting "without delay" of a task force to monitor the cessation of hostilities following reports of airstrikes targeting the moderate opposition.
Jean-Marc Ayrault spoke Monday, shortly before addressing a meeting of the Human Rights Council in Geneva. Staffan de Mistura, the UN envoy to Syria, had planned a meeting of the task force, led by the United States and Russia, for later in the day.
Ayrault told reporters he planned to discuss the "attacks including by air" with de Mistura and Ban. Critics say Russia and Syrian forces have been targeting the moderate opposition.