The U.S. is sending more troops and military hardware to the Middle East as it seeks to increase the resources available to "defend Israel," the Pentagon said in a statement.

U.S. Defense Secretary Lloyd Austin "reiterated the United States' commitment to take every possible step to defend Israel and noted the strengthening of U.S. military force posture and capabilities throughout the Middle East in light of escalating regional tensions," the statement, issued Sunday by Pentagon press secretary Maj. Gen. Pat Ryder, said.

This includes sending a guided-missile submarine to the region, as well as accelerating the transit of a carrier strike group equipped with F-35C fighter jets.

The statement follows a call between Austin and Israel's defense minister, Yoav Gallant, on Sunday. It comes against the backdrop of Iran's leadership vowing retaliation against Israel after the killing of Hamas' former political chief Ismail Haniyeh in Tehran on July 31.

Iran, which supports Hamas, says Israel carried out the assassination. Israel has not commented on the matter.

Tehran has not yet responded militarily to the act, leaving its adversaries and the wider region on tenterhooks.

The Biden administration has come under fire for its support of Israel, with critics saying that the U.S. should be using its leverage to enforce a cease-fire and should halt its supply of arms to the Jewish state. Biden has himself criticized the Israeli offensive as "over the top" and repeatedly said that "too many" civilians have been killed.

More than 100,000 voters in the Michigan Democratic primary in February, for instance, cast "uncommitted" ballots, sending a message that this issue will remain consequential to voter support for the Democrats in the November presidential election.

At the same time, many Democratic voters strongly support Israel, leaving the party's nominee, Kamala Harris, in a challenging position.

An all-out war between Israel and Iran — and Iran's proxies, such as Lebanese militant group Hezbollah — would be devastating to all sides involved. Each country's leaders continuously face pressure to respond militarily.

Tit-for-tat exchanges of missile strikes between Iran and Israel in April involved attacks that were essentially measured and telegraphed to avoid significant damage or casualties. Tehran has so far expressed scant interest in going to war with Israel, but some analysts warn that a forthcoming retaliation may be more severe.

Tensions between Israel and Iran have soared ever since the Hamas-led Oct. 7 attack on Israel that killed some 1,200 people and took a further 253 hostage, 116 of whom have since been freed.

Israel's military response to the attack has killed more than 39,000 people in the Gaza Strip, local health authorities say. Half the buildings in the blockaded enclave have been destroyed, according to the U.N.

The death of Haniyeh, who led cease-fire talks for Hamas, has also raised questions over the future of a diplomatic solution to the conflict between the Palestinian militant group and Israel. Hamas has chosen Yahya Sinwar as the group's new political leader. Sinwar, who also holds close ties to Iran, is seen as far more extreme than his predecessor and less willing to compromise on a cease-fire deal.