Israel closed its goods crossing with the Gaza Strip on Tuesday after militants in the Hamas-run territory fired rockets into the Mediterranean and launched incendiary balloons over the border.
The Kerem Shalom crossing will be closed until further notice to all traffic except humanitarian equipment and fuel, said the Defence Ministry unit that oversees the crossings.
"In the south, Hamas is continuing to enable explosive balloon attacks to be launched into the state of Israel," Defence Minister Benny Gantz said on Tuesday morning.
"We are not prepared to accept that and have closed the Kerem Shalom border crossing as a result."
Israeli fire services in the south of the country reported 60 fires caused by balloons on Tuesday, but there were no casualties.
"There will be a very heavy price for the balloon terrorism. We shall not tolerate it," Prime Minister Benjamin Netanyahu said during a visit to an air force base on Tuesday.
Hamas denounced the Kerem Shalom closure as an "aggressive" move that showed Israel's "insistence on laying siege" to Gaza.
It said it could cause further worsening of the humanitarian situation in the coastal strip.
The Palestinian territory has been under an Israeli blockade since 2007.
Explosives tied to balloons and kites were first used as a weapon in Gaza during intense protests in 2018, when they drifted across the border each day, causing thousands of fires in Israeli farms and communities.
Recent balloon attacks into Israel prompted retaliatory strikes against Hamas.
Hamas fired rockets into the sea on Monday after repeated exchanges of fire with Israel in recent days, Palestinian security sources said.
The rockets were a "message" to Israel that armed groups in Gaza would not "remain silent" in the face of an Israeli blockade and aggression, a source close to Hamas said.
As the Kerem Shalom crossing closed, the Rafah crossing between Gaza and Egypt opened on Tuesday for the first time since April.
It was closed to prevent the spread of the coronavirus.
Traffic in both directions was to be allowed for three days, letting Gazans leave the crowded, poverty-stricken strip for the first time since the start of the pandemic.
The World Bank says about 53 per cent of Gaza's population lived below the poverty line before the coronavirus crisis.
That number could rise above 60 per cent because of the economic fallout from the pandemic, it has said.
Hamas and Israel have fought three wars since 2008.
Despite a truce last year backed by the UN, Egypt and Qatar, the two sides clash sporadically with rockets, mortar fire or the balloons.
Palestinian analysts say fire from Gaza often aims to pressure Israel to allow the transfer of Qatari financial aid to Hamas.