The United States will continue to provide military aid to Israel, Defense Secretary Lloyd Austin said Thursday, playing down the idea of "red lines," even as he warned that an all-out conflict between Israel and Hezbollah would be devastating.

Israel rejected global calls for a cease-fire with Lebanon's Iran-backed Hezbollah on Thursday, defying its biggest ally, the U.S., and pressing ahead with strikes that have killed hundreds in Lebanon and heightened fears of a regional war.

Asked about "red lines" for U.S. support to Israel, Austin told reporters that the U.S. would not change its commitment to help Israel protect itself. He echoed U.S. calls for a cease-fire and a diplomatic solution to the crisis.

"We've been committed from the very beginning to help Israel, provide the things that are necessary for them to be able to protect their sovereign territory and that hasn't changed and won't change in the future," Austin said after a meeting in London with his British and Australian counterparts.

Israel said on Thursday it had secured an $8.7 billion aid package from the United States to support its military.

Austin said that there was a risk of all-out war between Hezbollah and Israel but added that a diplomatic solution was still viable.

"We now face the risk of an all-out war. Another full-scale war (could) be devastating for both Israel and Lebanon," Austin said.

"So let me be clear, Israel and Lebanon can choose a different path, despite the sharp escalation in recent days, a diplomatic solution is still viable," Austin said.

He added that the quickest way for Israel to achieve its goal of returning citizens to their homes in northern Israel was through diplomacy.

Israel has vowed to secure its north and return thousands of citizens to communities there, who have evacuated since Hezbollah launched a campaign of cross-border strikes last year in solidarity with Palestinians in Gaza.