The United States accused Iran on Monday of "actively facilitating" attacks on U.S. forces in the Middle East as it confirmed it had sent a small number of military advisers to Israel.

U.S. concerns have been rising about the potential for escalation of the war between Israel and Hamas militants, although Washington has rejected calls for a cease-fire as it says that ally Israel has a right to self-defense.

"Iran continues to support Hamas and Hezbollah, and we know that Iran is closely monitoring these events and, in some cases, actively facilitating these attacks and spurring on others who may want to exploit the conflict for their own good or for that of Iran," National Security Council spokesman John Kirby told reporters at the White House.