JERUSALEM - A Hamas commander was killed and an Israeli soldier was seriously injured Wednesday in clashes along the Israel-Gaza border, Israeli military and Palestinian officials said.

It was the most serious outbreak of violence in the area since a 50-day war in the summer.

The Israeli military said the clashes started when one of its patrols came under fire from a sniper inside the Gaza Strip, a coastal enclave ruled by the Islamist militant group Hamas. In response, Israeli jets and ground forces targeted Hamas's military positions in the southern part of the strip.

The clashes came after a similar but less intense exchange of fire Friday, when Israeli military aircraft hit a Hamas base in Gaza in response to the launching of a rocket into Israeli territory. There were no reports of casualties in that case.

Since the summer conflict ended in late August, there have been several reports of Gaza militants firing rockets and of Palestinians being injured or killed by the Israeli military near the border fence. Sniper attacks on Israeli patrols near the Gaza border also are not unusual; a month ago, shots were fired from Gaza near the Erez crossing between Israel and the strip.

Lt. Col. Peter Lerner, an Israeli army spokesman, called Wednesday's sniper attack a "lethal violation of the relative quiet along the Gaza border" and "a blatant breach of Israel's sovereignty." He said the army would continue to use all necessary means "to maintain the safety of the citizens of southern Israel and would not hesitate to respond to any attempt to harm its soldiers."

Prime Minister Benjamin Netanyahu said in a statement that Israel would respond firmly to "every attempt to disrupt the quiet in the south."

The injured soldier was from the Bedouin Reconnaissance Unit, the army said. Orders were issued to farmers to stay away from the border fence.

In Gaza, local media outlets said Taisir Sumairi, a commander in Hamas's lookout unit, was killed. A number of other Palestinians were injured in the clashes.

A Hamas statement said the group held Israel fully responsible for the escalation in the Gaza Strip and called the incident a "violation of the cease-fire after a series of provocations," including military incursions, and firing on fishermen and farmers, as well as airstrikes.

Hamas said that it had "called on all parties to stop the aggression" and that Palestinian factions would meet to discuss the incident.

The escalation in tension comes as Gazans try to rebuild the strip after the devastating summer war, which destroyed thousands of buildings and left tens of thousands of people homeless. International donors pledged $2.7 billion at a meeting in Cairo in October to help rebuild Gaza, but Palestinians say they have received little.

Additionally, the border crossing from Egypt into the strip has remained mostly closed since the war, and Israel tightly controls goods going into Gaza from its side.