Flooding the dozens of tunnels that run along the short Gaza-Egypt border was a rare act of tension between the Hamas government and their ideological parent, the Muslim Brotherhood, which now dominates Egypt's government.
The Egyptian effort appears to be aimed at closing down the illegal routes to better control what is going in. It follows an Egyptian-brokered deal that eased Israeli restrictions on building material going into Gaza.
Yousef Rizka, an adviser to the Hamas prime minister, urged Egypt to allow the tunnels to operate until restrictions on imports to Gaza are lifted.
Israel and Egypt have restricted the movement of people and goods in and out of Gaza since the militant group Hamas seized power of the territory six years ago. Much of the blockade has been loosened over the years, but residents still rely on the tunnels to get vital goods that are otherwise difficult to obtain in Gaza, such as construction materials and cheap fuel.
The tunnels have kept a modest construction boom flowing in Gaza that employs thousands of people, while an estimated 2,000 men and boys work in some 250 border tunnels.
But the tunnels are also easy conduits for weapons and militants to pass in and out of Gaza and the nearby lawless Sinai desert peninsula. From Sinai, militants have launched attacks against Egyptian and Israeli forces.
Smugglers said Egyptian military forces were digging water wells and pumping wastewater toward the smuggling area for the past two days.
One smuggler said he had to halt operations and rush his workers out after his tunnel filled with sewage. He declined to be named, fearing he would be identified by Egyptian forces. An Associated Press photographer at the scene saw at least 15 tunnels also flooded with wastewater.
Still, more than one hundred tunnels were operational, smugglers said.
"Tunnels are a lifeline for the people of Gaza," Rizka said. "Egyptian security authorities should halt any acts against the tunnels until we have official crossings above ground to provide the Palestinians with their needs. Otherwise Gaza will suffer."
An Egyptian military official in Sinai said the operation to flood the tunnels began Feb. 3. He added that they have also confiscated "large quantities of goods," including steel, cement, flour, sugar, fruit and computers.
The official, who spoke anonymously because he was not authorized to speak to media, said the military digs large holes on top of the tunnels then floods them with sewage water to make them collapse. He said there was concern that Egyptian and Palestinian smugglers may respond violently.