The Latest on Syria's civil war and peace talks in Geneva (all times local):

3:45 p.m.

The International Commission for the Red Cross says that together with the U.N. it is delivering its largest ever humanitarian aid convoy, destined for an opposition-held town under siege in central Syria.

ICRC spokesman Pawel Krzysiek says Thursday's aid convoy is the first to reach the town of Rastan in over a year. Krzysiek says the population of Rastan, which is in Homs province, has doubled because of the influx of people fleeing nearby fighting.

He says the convoy is made up of 65 trucks containing food, medicine and medical equipment, electricity generators and water treatment materials.

The two-month-old cease-fire, now in jeopardy, was intended in part to improve access to besieged areas of Syria. The U.N.'s humanitarian office said earlier this month that 21 percent of the nearly half million people in besieged areas of Syria were reached in March, down from 25 percent in February.

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3:00 p.m.

Russian foreign ministry spokeswoman Maria Zakharova says the suspended participation of the Syrian opposition in the Geneva talks could lead to "a return of total armed conflict"

Zakharova said on Thursday that "we have a situation where terrorists are desperately trying to disrupt the political process," referring to the Syrian opposition's High Negotiations Committee, which said Monday it was halting its involvement in talks.

Speaking at a press briefing in Moscow, Zakharova said the armed standoff in Syria is growing, especially to the north and south of Aleppo, though the U.S.- Russia brokered cease-fire agreement is generally holding in most parts of the country.

The spokeswoman blames Turkey for continuing to destabilize Syria by colluding with extremist groups

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1:30 p.m.

NATO Secretary-General Jens Stoltenberg says Syria's fragile cease-fire remains best the hope for ending the conflict.

Speaking in the Turkish capital, Ankara, he said the cease-fire was "under strain" but remains the "best basis for a negotiated, peaceful solution to the crisis."

Stoltenberg noted that Russia has maintained a "considerable military presence" in support of the Syrian government despite announcing a partial withdrawal.

A February cease-fire agreement between President Bashar Assad's government and rebel fighters, which excluded extremist factions like the Islamic State group, greatly reduced violence in Syria but has all but collapsed in the north of the country amid faltering peace talks in Geneva.