Palestinian militants fired dozens of rockets into Israel and the Israeli military carried out scores of air strikes as fighting near the Gaza-Israel border intensified overnight into Thursday.

Air raid sirens sounded almost nonstop in southern Israel from sundown on Wednesday, warning residents to stay in shelters as more than 80 rockets were fired in their direction. At the same time Israeli aircraft struck 140 targets belonging to the Hamas Islamist goup that controls the Gaza Strip.

The flare-up came after officials on both sides had talked about potential progress in UN and Egyptian efforts to broker a truce to end months of simmering violence.

Israeli media reported several residents of Sderot and other border towns were wounded by rocket fire.

In Gaza, one Hamas militant was killed in the air strikes, as was a Palestinian woman and her 18 month old child, Palestinian officials said. At least five other civilians were also wounded.

"I am deeply alarmed by the recent escalation of violence between Gaza and Israel, and particularly by today’s multiple rockets fired towards communities in southern Israel," said U.N. Middle East envoy Nickolay Mladenov in an overnight statement.

The U.N., he said, has engaged with Egypt in an "unprecedented effort" to avoid serious conflict, but warned "the situation can rapidly deteriorate with devastating consequences for all people."

Gaza has been controlled by Hamas for more than a decade, during which time it has fought three wars against Israel, most recently in 2014. Though neither side appears keen on another full-blown conflict.

Israeli Prime Minister Benjamin Netanyahu called off a trip to Colombia this week to attend to the Gaza truce talks and was due to convene his decision-making security cabinet on Thursday to discuss the situation.