A ceasefire declared nine days ago in the Gaza Strip became tense on Sunday as the Israeli military said it had launched airstrikes in response to attacks it said were carried out by Hamas militants on its forces.

But Hamas insisted it was adhering to the ceasefire, and one official accused Israel of creating"pretexts" to resume attacks.

Later on Sunday, the military said in an online press conference that it had carried out strikes following attacks in Rafah, in the southern Gaza Strip, and in the northern city of Beit Lahia, and warned that"the possibility of further strikes exists."

The Gaza Strip's Civil Defense Agency, which is under Hamas control, said at least 13 people had been killed across the territory. The Israeli military said it was verifying reports of casualties.

Israeli Prime Minister Benjamin Netanyahu earlier ordered security forces to take"strong action against terrorist targets in the Gaza Strip," his office said in a statement, accusing Hamas of"violating the ceasefire."

Defense Minister Israel Katz then warned that the group would "pay a heavy price for every shot and every ceasefire violation," adding that Israel's response would be "increasingly harsh."

An uneasy ceasefire in the Palestinian territories, brokered by US President Donald Trump and taking effect on October 10, halted more than two years of devastating war between Israel and Hamas. The deal set out the outlines of a hostage and prisoner exchange and was offered alongside an ambitious plan for the future of the Gaza Strip, but it immediately faced implementation challenges.

"Earlier today, terrorists fired anti-tank missiles and fire at IDF (army) forces" in Rafah, the military said in a statement.

"The IDF responded with fighter jet airstrikes and artillery fire, targeting the Rafah area," the statement added.

Palestinian witnesses told AFP that clashes broke out in the southern town of Rafah, an area still under Israeli control. One witness said Hamas was fighting a local Palestinian gang known as Abu Shabab, but the attackers were"surprised by the presence of army tanks."

Under Trump's 20-point plan, Israeli forces withdrew behind the so-called Yellow Line. They remain in control of about half of the Gaza Strip, including the territory's borders but not its main cities. Hamas, in turn, released 20 live hostages and is in the process of returning the remaining bodies.

At least 68,159 people have been killed in the Gaza Strip since the Hamas attack on Israel on October 7, 2023, according to the Hamas-run territory's health ministry, which the United Nations considers reliable. The figures do not distinguish between civilians and militants, but they show that more than half of the dead are women and children.

Hamas attacks on Israel in 2023 killed 1,221 people, mostly civilians, according to an AFP tally based on official Israeli figures.

Israel halts aid deliveries to Gaza Strip

Israel has closed its crossings into the Gaza Strip to aid convoys, a security official told AFP on Sunday, accusing Hamas of violating the ceasefire.

"Following Hamas' clear violation of the agreement, humanitarian aid deliveries to the Gaza Strip have been suspended until further notice," the official said.