The United States has stepped up contingency planning in case Israel launches a military strike on Iran's nuclear facilities, the Wall Street Journal reported on Saturday.

According to the report, U.S. defense officials are becoming increasingly concerned that Israel is preparing to carry out such a strike.

"Our concern is heightened," a senior U.S. military official told the Wall Street Journal.

The U.S. military is reportedly preparing for a range of possible responses to an Israeli strike on Iran, including attacks by pro-Iranian Shiite militias against the U.S. Embassy in Iraq.

The report said that, largely as a deterrent to Iran, the U.S. has 15,000 soldiers in Kuwait and has moved a second aircraft carrier strike group to the Persian Gulf region.

Additionally, the U.S. has been pre-positioning aircraft and other military hardware and has accelerated arms transfers to U.S. allies in the Persian Gulf region.

According to the report, top U.S. officials, including President Barack Obama and Defense Secretary Leon Panetta, have sent a series of private messages to Israeli leaders warning about the consequences of a strike on Iran. The U.S. reportedly wants to give sanctions and other measures more time, as part of efforts to compel Iran to abandon its alleged work to build nuclear weapons.

Obama and Prime Minister Benjamin Netanyahu spoke by telephone on Thursday and General Martin Dempsey, the chairman of the Joint Chiefs of Staff, will visit Israel next week.

Read this article in Hebrew