Defense Secretary Lloyd J. Austin III spoke with his Israeli counterpart, Yoav Gallant, on Sunday, the third call the two are known to have held in a week, amid rising fears of an escalation in the conflict between Israel and Iran.

In the call, Mr. Austin “reiterated the United States’ commitment to take every possible step to defend Israel,” according to a summary provided by the Pentagon press secretary, Maj. Gen. Patrick Ryder.

In an unusual disclosure, General Ryder said that Mr. Austin had ordered the ballistic-missile submarine Georgia to the Middle East. The Pentagon rarely announces the movements of its submarine fleet, underscoring the seriousness of the regional crisis.

General Ryder noted that Mr. Austin had already ordered additional combat aircraft and missile-shooting warships to the region. The orders came in response to threats from Iran and its proxies in Gaza, Lebanon and Yemen to attack Israel to avenge the assassination of a top Hamas leader, Ismail Haniyeh, in Tehran on July 31.

Mr. Austin has also directed the aircraft carrier Abraham Lincoln, equipped with F-35 fighter jets, to speed to the region, joining the aircraft carrier Theodore Roosevelt and its accompanying warships already in the Gulf of Oman.

A statement from the Israeli government said that Mr. Gallant had spoken to Mr. Austin about the Israeli military’s “readiness and capabilities in the face of threats posed by Iran and its regional proxies.”

The Israeli defense minister also discussed “the urgency of achieving an agreement for the release of hostages and thanked the U.S. administration for its leadership and commitment to this issue,” the statement said. The United States and Arab mediators are preparing to present what they have called a “final” proposal for a cease-fire in Gaza at a meeting on Thursday in the Middle East that Israel has said its negotiators will attend. Hamas has not indicated whether its representatives will be at the meeting.

The call between Mr. Austin and Mr. Gallant came a day after an Israeli airstrike hit a school compound in northern Gaza where displaced Palestinians were sheltering, an attack that Gazan authorities said killed dozens of people. Mr. Austin used the call to once again underscore the importance of “mitigating civilian harm” during Israeli operations in the enclave, General Ryder said.