Once a profitable business, Abu Abdullah's tunnel under the border between Egypt and the Gaza Strip has been out of work for three weeks due to an Egyptian security crackdown on smuggling. The Palestinian network of some 3,000 tunnels, created to thwart Israel's blockade of the coastal territory ruled by Hamas Islamists, was reduced to hundreds by bombing during Israel's three-week offensive in January. Now Egyptian police efforts are also biting into Gaza's underground supply system, which supplements the tightly restricted flow of aid commodities allowed in by the Israelis.

"Tunnel business has dropped to 20 percent of what it was before the war on Gaza due to Israeli destruction and the stepped-up security campaign by Egypt," said Abu Abdullah.

The Egyptian effort was "more effective" than Israeli bombs, he said. They not only blow up the tunnels but also stop contraband goods reaching Egyptian cities near Gaza.

Accused in the past of turning a blind eye to the smuggling operations, Egypt is cooperating along with US help in a bid to stop the contraband, which Israel says includes rockets that Gaza fighters use against Israel.

Israel has maintained a blockade of Gaza since Hamas was victorious in the 2006 parliamentary elections. The blockade was tightened after Hamas seized control of Gaza in a move some have said pre-empted a US-backed Fatah effort to expel Hamas from the enclave.

"We know the Egyptian police established checkpoints to stop shipments coming to the tunnel areas," Abu Abdullah told Reuters. "They ambushed trucks at tunnel shafts and they confiscated the goods before they bombed the tunnel."

Gaza relies on daily supplies of international aid, which is delivered via Israel and subject to Israeli approval.

The smuggled merchandise is mostly food, clothes and medicine, tunnelers said, adding that Hamas security warned them against any smuggling of weapons and drugs.

Palestinian resistance groups, including Hamas, were believed to have their own tunnels, which had always been kept secret. Israel repeatedly urged Egypt to stop fighters from bringing weapons through the private tunnels network.

Gaza markets were once filled with electronic goods, water heaters and fans that are now in high demand as summer nears.

"Now all these do not enter Gaza," said Ahed Abu Ayman, who used to import the goods and sell to local merchants, sometimes at a high markup because of the added cost of smuggling them.

Supplies of fuel coming through the tunnels are down by half, according to traders. Gaza obtains fuel from Israel, but shipments have sometimes been arbitrarily cut off.

Yet the tunnel zone, on the edge of the southern Gaza city of Rafah, is still a hive of hidden activity. The hum of many generators rises from behind piles of sand, which conceal tents and shelters made of fabric and metal sheeting.

The tunnels run 7 to 15 meters below the surface and can be up to 1,000 meters in length.

Tunnelers say that the Egyptian authorities use drills and special American equipment to trace the course of the tunnels. Then they either blow them up or pump water inside to cause collapse. Tunnelers and Hamas also accuse Egypt of releasing gas inside tunnels as well in order to drive out Palestinians.

Medical workers said a Palestinian died when a tunnel collapsed on him last week. Dozens of others have been killed in the past year but tunnelers keep coming because young Palestinian men are desperate for work.

The Egyptians add to the already considerable physical risks run by Palestinians working the tunnels by sometimes filling them with gas, tunnelers said.

"I make $50 a day just to take dirt out of a tunnel and $100 when the tunnel operates and we get goods out," said Abu Ahmad, his faced masked by a black T-shirt. "Destiny is in God's hands."

"I have shares in this tunnel," said Abu Islam, a young light-bearded man. "I am saving money to get married. I think I need another five months before I can hold my wedding." Abu Abdullah, a father of four and employer of a crew to maintain and operate his tunnel, said his business was suspended when Egyptian police discovered a shaft on their side of the border adjacent to the shaft of his line.

Now workers are making a detour and digging an additional 100 meters to open a new shaft.

"We have no choice but to continue with this work. The needs of Gaza market are greater every day," he said.