BEIRUT (AP) — Syrian activists say government warplanes are bombarding opposition-held parts of the northern city of Aleppo even as the United Nations is calling for a "humanitarian pause" in fighting so that electricity and water networks can be repaired.

Tuesday's airstrikes and shelling came as rival parties brought in reinforcements to Aleppo ahead of an expected new round of fighting after militants breached a government-imposed siege and cut a key government route to the contested city over the weekend.

Two U.N. aid officials, Yacoub El Hillo and Kevin Kennedy, said in a statement that the water and electricity infrastructure has been damaged in the fighting.

They say that since the militants' offensive, the total number of civilians living in "de facto fear of besiegement" has increased to over two million.