An Israeli airstrike killed four people in Beirut early Tuesday, the Lebanese Health Ministry said, rocking an already shaky ceasefire between Israel and Hezbollah.

Israel’s army has urgently warned people to evacuate parts of a Beirut suburb as it vowed to retaliate against strikes which it said were launched from Lebanon into northern Israel

The command for people to leave parts of the suburbs south of the Lebanese capital where Hezbollah holds sway is the first since a cease-fire went into effect in November.

Saudi state media says Lebanon and Syria have signed an agreement on border demarcation and to boost coordination between the two countries regarding security along their tense frontier.