Three officers were killed on Tuesday when explosions struck two police checkpoints in the Gaza Strip, the Hamas-run interior ministry said. Several Palestinians were injured in the attack. Interior ministry spokesman, Eyad Al-Bozom, said security forces were making progress in their pursuit of those behind the explosions, but he did not disclose further details. “The sinful hands that carried out this crime will not escape punishment,” said Bozom. Such attacks on Hamas were rare. A spokesman for the Israeli military said he knew of no involvement by Israel in the back-to-back incidents in Gaza city at a time of simmering cross-border confrontations with Hamas. The Israeli military earlier Tuesday bombed a Hamas military post after militants in the strip fired a mortar round across the border but said it had not carried out any air raids at night. Palestinian eyewitnesses at the scene told AFP they had seen no aircraft overhead. The first blast destroyed a motorcycle as it passed a police checkpoint, witnesses said, according to Reuters. Two police officers were killed and a third Palestinian wounded. It was not immediately clear if the riders were among the casualties. The second explosion, less than an hour later, killed one officer and wounded several people at a police checkpoint elsewhere in the city, the interior ministry said. The ministry declared a state of emergency throughout Gaza, putting security forces on alert. AFP journalists reported an increased Hamas presence on the main roads of the enclave. Tuesdays events were the latest in a string of cross-border incidents that have raised concerns of further escalation before Israels 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 strips main power station, meaning a cut to Gazas already meager electricity supply.