Egypt yesterday denied accusations by Hamas that it had pumped toxic gas into smuggling tunnels between Gaza and Egypt, killing four Palestinians and injuring three.

An Egyptian intelligence official said that Egypt had blown up the entrances to several tunnels earlier this week in an effort to seal them off. He added that the blasts may have sparked a fire that sucked air out of the tunnels, suffocating the workers.

Egypt has come under intense pressure from Israel to prevent Palestinians from defying an Israel-led blockade to bring in arms, medical supplies and other non-essential goods.

Hamas, the Islamist group that controls the Gaza Strip, insisted Egyptian soldiers had dispersed toxic gas in the tunnels, killing labourers. “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,” the Hamas spokesman Sami Abu Zuhri said.

Palestinian doctors working for the Hamas-run health ministry claimed that the four labourers had died from suffocation and showed traces of gas poisoning. Underground smuggling tunnels provide a crucial lifeline for the 1.5 million residents in the impoverished Gaza Strip, whose borders have been sealed off by Israel since Hamas seized control in the tiny coastal territory in 2007. Scores of workers have been killed by frequent tunnel cave-ins, while Israel has bombarded the tunnels in response to rocket attacks aimed at its territory.

Egypt, whose relationship with Hamas is increasingly strained, is building an underground steel wall that will sever all but the deepest tunnels. Hamas has criticised Egypt for supporting Israeli policies when Palestinian civilians are harmed. Up to 1,400 were killed during Israel’s offensive in Gaza 16 months ago.