He said that the tunnels are poorly constructed.

"Many of them collapse. In fact, more than 45 Palestinians have died in cave-ins. More than 40 has died as a result of direct attacks by the Egyptians in these attempts to stop [smuggling].

Vital supplies

The 1.5 million population of Gaza has relied on the vast network of tunnels from Egypt for vital supplies since Israel put the territory under siege after Hamas came to power there in June 2007.

The interior ministry of the Hamas government said the tunnel workers had been killed by toxic gas pumped into the tunnel.

"This is a terrible crime committed by Egyptian security against simple Palestinian workers who were trying to earn their daily bread"

Fawzi Barhoum,
Hamas spokesman

"The interior ministry confirms that the citizens' cause of death was the Egyptian security forces spraying poison gasses into one of the tunnels," it said in a statement.

A Palestinian police official said three people died of smoke inhalation and a fourth from flying debris caused by explosives being detonated in the tunnel. 

Another three tunnel workers were admitted with injuries to a hospital in the Egyptian town of Rafah, he said.

Medics said as many as 10 people had been injured when the tunnel collapsed.

A Hamas official demanded an explanation for the incident.

"This is a terrible crime committed by Egyptian security against simple Palestinian workers who were trying to earn their daily bread," Fawzi Barhoum, a Hamas spokesman, told The Associated Press.

"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.

'Too many tunnels'

Egyptian security officials admitted that they had destroyed four tunnels north of the Rafah border crossing with Gaza on Wednesday.

Al Jazeera's Amr El-Kahky, reporting from Cairo, said the Egyptians said they had done what they should be doing by notifying the Palestinians that the tunnel were the casualties occurred was going to be demolished.

"The Egyptians say that there are too many tunnels on the 15km long border. There are about 1,300 to 1,500 tunnels in that area," he said.

Israel says the tunnels are used to smuggle weapons into the Gaza Strip [GALLO/GETTY]

"Most of these tunnels are dug with the approval by Hamas on the other side. They are not all operated by people who are pro-Hamas ... They are also operated by outlaws on both sides of the border and that's why it is very difficult to keep controlling what goes in and what goes out.

"Egypt thinks a lot of things come from Gaza, including people that could destabilise the security situation in Sinai."

The United States and Israel have been pushing Egypt to do more to close the tunnels, which which they say are used to arm Palestinian fighters.

Israeli aircraft have bombed the tunnels in the past, particularly during the country's three-week assault on Gaza, which ended in January last year.

Palestinian officials in Rafah say Egypt has stepped up a crackdown on smuggling in recent months, blowing up numerous tunnel entrances on its side of the border, setting up checkpoints in the area and confiscating contraband.

Since December, Egypt has also been building an underground steel wall to block the tunnels.