The United States is already heavily involved in the conflict between Israel and the Palestinians and must be held to account, an Iranian official said on Monday.

The U.S. is bolstering its firepower in the Middle East in response to war between its ally Israel and the Iranian-backed Palestinian militants Hamas amid fears of regional spillover.

Asked if Tehran would engage if the U.S. weighed in, Foreign Ministry spokesperson Nasser Kanaani said: "Iran considers that the United States is already militarily involved in the conflict between Israel and Palestinians."

"The crimes of the Zionist regime are carried out with the support of the United States and Washington must be held accountable," he added at a news conference.

The newest U.S. aircraft carrier - also the world's largest - is already in the eastern Mediterranean and is due to be joined by a second U.S. aircraft carrier in coming days.

U.S. Secretary of State Antony Blinken said on Sunday the aircraft carriers are not a provocation but a deterrence.