ALSO SEE: US Military Death Toll Rises to 6

The United States evacuated diplomats across the Middle East and shut down some embassies as war with Iran intensified Tuesday while President Trump signaled the conflict could turn into extended war.

Israel said it sent ground forces across the border into south Lebanon and bombed Beirut suburbs as fighting with Hezbollah resumed after more than a year.

The U.S. and Israel kept up their attacks in Iran. Explosions were heard in the Iran's capital and other parts of the country.

Trump said Monday that the war could last four to five weeks, then said later that the U.S. had "the capability to go far longer" than that.

In a social media post, Trump said that the U.S. had a "virtually unlimited supply" of munitions.

"Wars can be fought 'forever,' and very successfully, using just these supplies," Trump wrote.

The war has so far killed six U.S. service members, according to U.S. officials who have warned there are expected to be more casualties.