Egyptian forces pumped gas into a cross-border tunnel used to smuggle goods into the Gaza Strip late on Wednesday, killing four Palestinians, Hamas officials said.
Under pressure from Israel and the United States, Egypt has tried to stem the secret passages from its Sinai peninsula, which have allowed Palestinians in Gaza to import weapons and commercial goods in defiance of an Israeli-led blockade.
Israel and Egypt have kept Gaza's official border crossings closed since Hamas seized control of the coastal strip in 2007 from forces loyal to Western-backed Palestinian President Mahmoud Abbas, who now only governs in the West Bank.
A Hamas security official in charge of the tunnel area along the border said the Egyptians filled the passage with some type of crowd dispersal gas. He spoke on condition of anonymity because he was not authorized to give his name.
The Hamas Interior Ministry later said in a statement the gas used to try to clear the tunnel was poisonous. Besides those killed, six people were injured, it said.
"The Interior Ministry confirms that the citizens' cause of death was the Egyptian security forces spraying poison gasses into one of the tunnels," the statement said without elaborating.
A doctor at a hospital in the Gaza border town of Rafah, Hamdan Abu Latifa, said the dead smugglers suffocated.
An Egyptian border security official refused to comment Wednesday. Egypt, now building an underground wall along the frontier, does not generally discuss its anti-tunneling efforts.
Egyptian security forces have sprayed gas into tunnels before, according to Hamas officials and tunnel operators. But Wednesday's incident was the first time people have died as a result, they said.
Condemnation from Hamas
"This is a terrible crime committed by Egyptian security against simple Palestinian workers who were trying to earn their daily bread," Hamas spokesman Fawzi Barhoum to The Associated Press. "It was a killing in cold blood. Hamas and all the Palestinian people condemn it strongly."
"We demand that Egypt explain its position about what is happening and investigate the circumstances of this terrible crime and show the truth to the entire world and hold those responsible accountable," he said.
Israel says Palestinian militants use tunnels to smuggle weapons into Gaza. But the 1.5 million residents of the impoverished Strip also rely on the tunnels to bring in food and commercial goods like refrigerators and clothing.
Israeli aircraft have targeted the tunnels in bombing runs in the past, particularly during its military offensive against Gaza more than a year ago.