GAZA (Reuters) – Palestinian militants in the Gaza Strip fired two mortar shells into southern Israel on Friday in the latest challenge to a ceasefire deal that the enclave’s Hamas rulers have vowed to uphold.

The shells landed in a farming community near the border with the Gaza Strip, causing no casualties, an Israeli police spokesman said.

There was no immediate claim of responsibility for the cross-border fire, the fourth such incident since the Egyptian-brokered ceasefire took effect on June 19.

The mortars were fired a day after Hamas issued its sternest warning yet to militant groups to abide by the truce.

Israel has kept border crossings used to bring humanitarian and commercial supplies into the Hamas-controlled Gaza Strip closed since Wednesday but it allowed fuel to reach the territory’s sole power station on Friday.

A European Union official said an estimated 600,000 liters of industrial fuel would be pumped through the Nahal Oz border terminal to Gaza’s power station, enough to keep the plant running for several days.

The EU funds fuel deliveries to the power station.

Israel closed the border crossings after Palestinian militants fired rockets into the Jewish state on Tuesday.

The Islamic Jihad militant group said the rocket attack was in retaliation for the Israeli army’s killing of one of its commanders in the occupied West Bank.

Both sides have been trading blame for breaching the ceasefire agreement, which is backed by the West with the aim of advancing Israeli-Palestinian peace talks that have shown little outward sign of progress.

The ceasefire deal calls for Hamas to stop cross-border rocket fire and for Israel to gradually ease its embargo on the Gaza Strip.