Israel tightened its blockade of the Gaza Strip yesterday, partly over kites carrying firebombs to set alight Israeli farmland, as concerns mounted over whether the rudimentary devices could spark another war.

Days after the heaviest exchange of fire between Israel and Palestinian militants in Gaza since a 2014 conflict, Israel said it was blocking until Sunday fuel deliveries to Gaza through its only goods crossing with the enclave.

The fishing zone enforced by Israel off the Gaza Strip was also reduced from six nautical miles to three.

The goods crossing, known as Kerem Shalom, will remain open for food and medicine on a case-by-case basis.

It had already been closed to most deliveries since July 9, partly in response to the firebombs.

The move followed months of tension that has raised the possibility of a fourth war between Israel and Gaza militants since 2008.

Beyond the kites and last weekend's exchange of fire, mass protests and clashes along the Gaza border since March 30 have seen dozens of Palestinians shot dead by Israeli soldiers.

Hamas, the Islamist movement that runs the Gaza Strip, was further backed into a corner by the Israeli closure, with humanitarian conditions in the enclave of two million people already badly deteriorating.

Gaza's only other border crossing, with Egypt, was also closed on Tuesday, an AFP journalist reported, but there was no official statement explaining why.

That prompted speculation that Egypt, which has mediated between Israel and Hamas, had closed it to add to pressure on the Islamists to clamp down on the arson kites.

The crossing, known as Rafah, has been largely closed in recent years, though Egypt had kept it mostly open since mid-May.

Israel has in recent days pledged a firmer response to the hundreds of arson kites and balloons that Palestinians have flown over the border fence since April.

Prime Minister Benjamin Netanyahu, under political pressure over the issue, has ordered the military to stop the firebombs -- raising the question of how that can be achieved.

Hamas has slammed Israel's closure of the goods crossing as a "crime against humanity" and accused Israel of exaggerating the threat from arson kites.

Israel's fire service says around 750 fires have burned some 2,600 hectares (6,400 acres), estimating the damage at millions of shekels (hundreds of thousands of dollars or euros).