Hamas spokesman Sami Abu Zohri demanded an immediate probe into the incident at a press conference on Thursday and called on the Egyptian government to prosecute those in charge. He said that his movement strongly denounced the action against the Palestinian victims.

On Wednesday, medical sources at Al-Najar hospital reported that nine others had also been wounded.

At least 40 smugglers have been poisoned by noxious gases since a blockade was imposed on the Gaza Strip, said Abu Zohri.

He added that a total of 145 residents have been killed in different incidents.

He explained that Palestinians in the Gaza Strip need the tunnels because of the blockade.

“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.”

In Cairo, an Egyptian intelligence official denied the allegation. He said that security forces blew up the entrances to several tunnels earlier this week.

He said Egypt routinely blows up the entrances to seal the tunnels off. He said fires sparked by such explosions could use up all the oxygen in the tunnel and people caught inside could suffocate.

The official spoke on condition of anonymity because he was not authorized to speak to the media.

After Hamas took control of the Gaza Strip in June 2007, Israel imposed a crippling blockade on the territory and closed most of its commercial border crossings into Gaza.

This forced people in the area to dig a vast network of smuggling tunnels under the borderline between Egypt and Gaza so they could smuggle in vital supplies.

Israel says Palestinian fighters use tunnels to smuggle weapons into Gaza, and have ordered its warplanes to repeatedly bombard tunnels in the city of Rafah south of the Gaza Strip.

— With input from agencies