Israel and the U.S. are convinced Iran is preparing to retaliate for the Israeli strike on an Iranian consulate in Syria, U.S. officials say. 

Israel on Monday struck an Iranian consulate in Damascus, Syria, and killed a number of senior leaders of Iran's Islamic Revolutionary Guard Corps, according to the Pentagon.

The U.S. has picked up intelligence that Iran is planning a retaliatory attack that would include a swarm of Shahed loitering drones and cruise missiles. Officials say the timing and target are unknown, but a proportional response to the Damascus attack would be to hit an Israeli diplomatic facility. The attack is likely to come between now and the end of Ramadan next week.

Another important unknown is where the drones and missiles would be launched — from Iraq or Syria, which could prompt a thin claim of deniability by Tehran — or from Iranian territory. 

A public funeral was held in Tehran on Friday for the seven IRGC members killed in the suspected Israeli strike in Damascus, including two generals, CBS News' Seyed Bathaei reported.

At the funeral, the IRGC's overall commander, Gen. Hossein Salami, warned that Israel "cannot escape the consequences" of assassinating Iranian military officers, he did not give any further indication of how or when Iran might retaliate, Bathaei said.

Seeking to prevent Iranian retaliation on facilities connected to the U.S., Biden administration officials have stressed that the U.S. had no advance notice of the strike. 

National Security Council coordinator for strategic communications John Kirby said that President Biden in his phone call Thursday with Israeli Prime Minister Benjamin Netanyahu discussed Iranian threats to Israel. 

"There was discussion between the two leaders about the very viable and quite public threat Iran is making to Israel's security in the last day or so, and the president made very clear — very clear — to Prime Minister Netanyahu that he can count on U.S. support to help them in their self-defense against threats directly and publicly posed by Iran," Kirby told reporters on Friday. 

The Israelis are already warning publicly that they will retaliate, so an attack by Iran on an Israeli facility would be another step closer to a regional war.

Earlier Friday, Iranian presidential adviser Mohammad Jamshidi posted on X that Iran's message to American leaders was "not to get dragged in Netanyahu's trap for U.S.: Stay away so you won't get hurt." Jamshidi claimed that the U.S. then "asked Iran not to target American facilities."

CBS News confirmed that the U.S. did receive a written message from Iran. A State Department spokesperson told CBS that the U.S. responded by sending a written warning to Iran not to use the Israeli strike as a "pretext to attack U.S. personnel and facilities."

The State Department spokesperson characterized its message to Iran as a warning: "We did not 'ask.'"

It is unusual for the U.S. to comment on the context of diplomatic messages or discussions but Iran had publicly disclosed it. The Swiss government acted as a conduit for the written message since the U.S. and Iran do not have direct diplomatic ties.

The U.S. has roughly 900 troops in Syria, and 2,500 troops in Iraq, as well as other support outposts in Jordan. The Iraqi prime minister, Shia al-Sudani, is scheduled to visit the White House on April 15 to discuss the U.S. military presence.

David Martin is CBS News' National Security Correspondent.