A senior Hamas official has slammed America's decision to exercise its veto power against a United Nations Security Council draft resolution calling for an immediate ceasefire in the Gaza Strip, arguing the decision ran contrary to the ideals that Washington purports to promote on the world stage.

The United States on Wednesday vetoed a draft UN Security Council resolution that demanded an "immediate, unconditional and permanent ceasefire" between Israel and Hamas militants in Gaza and unhindered aid access across the war-torn enclave.

Mansour urged Israel to lift what he described as a "punitive, illegal siege” and to open all crossings to allow the unimpeded delivery of aid.