WASHINGTON (AFP) - The United States on Friday condemned as "tragic irony" the International Criminal Court's decision to open a preliminary probe into possible war crimes committed by Israeli forces against Palestinians.

"We strongly disagree with the ICC prosecutor's action today," State Department spokesman Jeff Rathke said in a statement.

"It is a tragic irony that Israel, which has withstood thousands of terrorist rockets fired at its civilians and its neighborhoods, is now being scrutinised by the ICC," he added.

The ICC's prosecutor on Friday opened the probe into the alleged war crimes, including during last year's offensive in Gaza. Nearly 2,200 Palestinians and 73 Israelis were killed during that conflict.

The Palestinians formally joined the ICC earlier this month, allowing them to lodge war crimes and crimes against humanity complaints against Israel as of April.

The United States has repeatedly said it does not believe that Palestine is a state and so should not be allowed to join the ICC. Israel immediately blasted the ICC decision as "scandalous."