Iran is preparing to attack Israel from its territory on Friday or Saturday but hasn't taken a final decision yet, the Wall Street Journal reported on Thursday evening as Israel braces for retaliation for an alleged Israeli strike that killed seven Iranian officers almost two weeks ago.

Amid a diplomatic offensive by the U.S. to prevent an escalation into an all-out regional war, Reuters reported that Iran transmitted a message through Oman, indicating it would respond through its regional proxies to prevent a major escalation.

An American source told the Arabic newspaper al-Arabiya that the U.S. would join forces with Israel in the case that Iran carried out a "disproportionate response," which would probably mean a missile or drone attack launched from Iranian territory directly against Israel.

"The projection of close U.S.-Israel military cooperation and the determination to respond forcefully to Iranian threats were missing ingredients just 48 hours ago," commented Richard Goldberg, senior adviser at the Foundation for Freedom of Democracies (FDD).

"The president's remarks yesterday and Gen. [Michael] Kurilla's visit today are critical resets in the political environment that Tehran must now factor into its calculus," he added.

In recent days, Iranian social media channels affiliated with the Revolutionary Guard Corps (IRGC) have been awash with videos showing simulations of drone or missile attacks against Israeli facilities, including the alleged nuclear facility in Dimona.

IRGC and Syrian advisers told the WSJ that Iran delivered more drones to its proxies in Syria and Iraq, to prepare them for possibly taking part in an attack on Israel.

According to the WSJ report, an informed U.S. official said Iran could attack Israel directly, as opposed to an attack on Israeli embassies around the world. Many embassies have taken additional security measures in anticipation of such an attack.

The U.S. also said its diplomatic personnel in Israel were barred from traveling outside the Tel Aviv, Jerusalem, and Beersheba areas, "out of an abundance of caution."

Iran could also attack targets in disputed Israeli territories in the Golan Heights or the Gaza Strip to be able to claim not to have attacked Israeli sovereign territory, the report said.

In the past few days, "several regional and European ministers" called Iran to try to prevent a regional escalation, an Iranian spokesman told the WSJ. Even Russia called Iran to "show restraint."

The commander of the U.S. forces in the Middle East, CENTCOM Cmdr. Gen. Kurilla, arrived in Israel on Thursday to coordinate possible responses to an Iranian strike, and will meet with the IDF Chief of Staff and the Israeli Defense Minister.

"A weak response to Iranian aggression would simply invite more of the same and risk more American or Israeli casualties. A review of history demonstrates that Tehran tends to back down when confronted with the resolute application of American military power," the FDD's Bradley Bowman said.

Israel's Defense Minister Yoav Gallant on Thursday also called his colleague, U.S. Defense Secretary Lloyd Austin for the second time this week.

They discussed the preparations for an Iranian attack, with Gallant emphasizing that the State of Israel would not tolerate an Iranian attack on its territory.