The Gaza Strip was in a “state of alert” on Wednesday after explosions killed two policemen in the Palestinian enclave, authorities said.

The officers died in “two explosions targeting police checkpoints” late on Tuesday night, the interior ministry in the Hamas-controlled coastal territory said in a statement.

The Israeli military denied carrying out an air strike, and Palestinian witnesses at the scene told AFP they had seen no aircraft overhead.

The Gaza Strip, home to two million Palestinians, was in a “state of alert,” the ministry said and AFP journalists reported an increased Hamas presence on the main roads of the enclave.

The authorities in Gaza did not specify the nature of the explosions.

The Israeli military earlier on Tuesday bombed a Hamas military post after armed fighters in the Strip fired a mortar round across the border but said it had not carried out any air raids at night.

Tuesday’s events were the latest in a string of cross-border incidents that have raised concerns of further escalation before Israel‘s September 17 elections.

Israeli Prime Minister Benjamin Netanyahu is fighting for re-election, with political opponents calling for tougher action against Hamas.

On Monday, Israeli warplanes hit what the military said were “terror targets in a Hamas military compound in the northern Gaza Strip, including the office of a Hamas battalion commander.”

Israel also announced it was slashing by half the fuel it pipes to the strip’s main power station, meaning a cut to Gaza’s already meagre electricity supply.

Israeli authorities have accused Hamas of being responsible for the latest violence, which undermines a truce brokered by the United Nations and Egypt that provides for an easing of the Israeli blockade of Gaza in return for an end to military operations from the Palestinian enclave.

Specifically, the Israeli army accuses Hamas of not doing enough to contain its ally Islamic Jihad, which is considered close to Iran, an enemy of Israel.

Since 2008, Israel has waged three wars on the Gaza Strip,  killing thousands of people, mostly Palestinian civilians.

Israel has long said it holds Hamas responsible for all violence from Gaza, while Hamas says Israel is responsible for the state of anger and pressure inflicted on Gaza’s residents due to the continued siege.

The Gaza Health Ministry said that since the start of the weekly Great March of Return protests last year, the Israeli army has killed more than 300 demonstrators and wounded 17,000 others, who were officially referred to hospitals.

Seven Israelis have also been killed.