Gaza City: Hamas movement on Thursday accused Egyptian security forces of killing four Palestinians by pumping poisonous gas into a cross-border smuggling tunnel.

"Hamas holds the Egyptian side responsible for the killing of four innocent workers after Egyptian security forces pumped poisonous gas into one of the tunnels," Hamas spokesman Sami Abu Zuhri told reporters in Gaza.

"We demand an investigation into the incident and for those responsible to be brought to justice."

Following the incident on Wednesday night, Egyptian security officials said their forces had destroyed four smuggling tunnels along the Gaza-Egypt border but were not aware of any casualties.

Palestinian medics working for the Hamas-run health ministry said the four had died from suffocation and that there was evidence of poisonous gas.

Gaza's 1.5 million people have largely relied on a network of hundreds of tunnels beneath the border with Egypt since Israel and Egypt tightened an already strict closure of the territory after Hamas seized power in June 2007.

Most of the tunnels are used to bring in basic goods like food, household appliances and livestock, but Hamas and other militant groups use their own more secretive tunnels to bring in arms and money.

Abu Zuhri said the territory's reliance on the tunnels had been imposed on it by the border closures, which keep out all but basic humanitarian aid.

"The alternative is not to kill innocent citizens but to open the crossings," he said, adding that some 40 workers had been killed by Egyptian security forces pumping poisonous gas and sewage into the tunnels.