JERUSALEM — Hezbollah fired into a disputed border zone held by Israel on Monday after multiple Israeli strikes inside Lebanon since a cease-fire took hold last week. The militant group said the volley, its first during the truce, was a warning shot in response to what it called repeated Israeli violations.

Hezbollah has claimed the first strike against Israel since a US-backed cease-fire plan came into effect less than a week ago, prompting Israeli officials to vow a strong response in the most serious threat so far to the truce with Lebanon.