The United Nations said Thursday it had halted cross-border convoys carrying desperately needed aid from Jordan to southern Syria over security concerns amid a barrage of air strikes on rebel-held towns. The UN has warned that more than 750,000 lives are at risk in the south, which is meant to be protected by a cease-fire put in place last year by Russia, Jordan, and the United States. GENEVA: The United Nations said Thursday it had halted cross-border convoys carrying desperately needed aid from Jordan to southern Syria over security concerns amid a barrage of air strikes on rebel-held towns. “The extremely effective lifeline across the border from Jordan has been discontinued due to the fighting in recent days,” the head of the UN’s Syria humanitarian taskforce, Jan Egeland, told reporters in Geneva. He said no aid convoys had crossed the border in the past two days. His comments came amid a barrage of Russian strikes on rebel-held towns in southern Syria, killing 22 civilians on Thursday alone, making it the bloodiest day yet of the government’s offensive in the strategic region. With Moscow’s help, Syrian President Bashar Assad’s army has battered the south for more than a week with air strikes, rocket fire and crude barrel bombs. The UN has warned that more than 750,000 lives are at risk in the south, which is meant to be protected by a cease-fire put in place last year by Russia, Jordan, and the United States. But now, President Bashar Assad has set his sights on retaking the area. “Tens of thousands of civilians are fleeing for their lives,” Egeland said, describing the situation as “heart wrenching, because this was a zone were people felt safe until just 10 days ago.” He urged Russia, Jordan and the United States to reestablish the de-escalation agreement they hammered out for the area last July, insisting “they can do it again.” “There is nothing inevitable about this escalation of fighting.” The bombardment has already forced more than 50,000 to flee their homes in search of safety, according to the UN, while others huddle in their basements to wait out the raids. Egeland said the fighting was “so intense” that the UN had failed to “reach sufficient agreements on safe passage for the convoys.” He called on “all who have influence on the situation,” including Russia, the United States and Jordan, “to do their utmost to ensure that we get that kind of assurance, and then the convoys will resume.”