GENEVA: Aid convoys for four Syrian towns will be postponed as staff reassess security after a deadly attack on relief trucks and intensified violence, a senior official from the International Committee of the Red Cross (ICRC) said on Tuesday.

Syrian or Russian aircraft struck an aid convoy near Aleppo, killing 12 people on Monday, a war monitor reported, as the Syrian military declared a one-week truce over.

"This is very worrying. We see a resumption of violence, an intensification of fighting in many locations," Robert Mardini, ICRC director for the Middle East and North Africa, told Reuters in Geneva.

"We had something planned in the four towns, but for now it is put on hold to reassess the security conditions," he said, referring to rebel-besieged Foua and Kefraya in Idlib and government-blockaded Madaya and Zabadani near the Lebanese border.

At least 18 of 31 trucks in a UN and Syrian Arab Red Crescent (SARC) convoy were hit on Monday along with an SARC warehouse, U.N. spokesman Stephane Dujarric said in New York. The convoy was delivering aid for 78,000 people in the hard-to-reach town of Urem al-Kubra in Aleppo Governorate, he said.

SARC's director in Urem al-Kubra, Omar Barakat, was among the dead, Mardini said. "The team is in shock."

"Omar was badly injured and rescue team could not reach him for two hours. When he was evacuated he could not survive his wounds," he said.

A separate SARC/ICRC convoy to Talbiseh in Homs province made its first delivery since July on Monday, carrying supplies for more than 80,000 people.

The team stayed there overnight due to intensified fighting, Mardini said.

"Inshallah, they will be on their way back to Homs this morning," he added.

"It is difficult to read the environment in coming hours because you have a mixture of intensification of fighting and politicisation of humanitarian aid ... It is high time to de-link humanitarian work from politics," Mardini said.