BEIRUT, Lebanon — A Syrian government assault on one of the country’s last two rebel-held territories has driven 160,000 people from their homes across southwestern Syria, violating a United States-backed cease-fire and threatening to entangle Israel and Jordan in the conflict.

Government troops, backed by Syrian and Russian airstrikes and barrel bombs, have steamrollered through several towns in eastern Dara’a Province over the past week, setting off the latest humanitarian calamity in the seven-year war and moving the government a step closer to consolidating control over the country.

The attack has ripped up a brittle cease-fire negotiated last year by Russia, Jordan and the United States, the Trump administration’s main peacekeeping achievement in Syria.

The United States, which has about 2,000 troops in Syria, has publicly criticized Russia for breaking the deal but has done little to enforce it, retreating from its initial warnings of “serious repercussions” for cease-fire violations and leaving southern rebels and civilians largely on their own.