Egypt’s closure of smuggling tunnels between the Sinai Peninsula and the Gaza Strip is costing Hamas $230 million in lost revenue every month, a senior official in the Islamist organization said on Sunday.

Hatem Oweida, deputy economy minister for Hamas, said that “closure of the tunnels caused heavy losses to the industry, commerce, agriculture, transport and construction sectors,” AFP reported.

The Egyptian army has been engaged in a determined campaign to stop smuggling operations, closing tunnels by either blowing them up or flooding them.

Hundreds of tunnels have been dug out since 2007, very close together, along the narrow sliver of land that forms the border between Egypt and Gaza. The tunnels gained importance after Israel and Egypt imposed a naval blockade on Gaza following Hamas’s military takeover there in 2006.

The tunnels, dug through the sand beneath the border, provide 40 percent of the construction and raw materials for the coastal enclave, Oweida said. He warned that, if the passages were not reopened, unemployment in Gaza could reach 43%.

Hamas reaped enormous revenue by taxing all goods that passed through the tunnels. In the past, the tunnel-digging industry employed up to 40,000 people, and provided nearly 40% of the government’s budget.

Earlier this month, Egyptian Border Police reported authorities had closed 1,055 tunnels since January 2011 — 794 of them in the nine months since January 2013.

Egypt clamped down on tunneling after it became clear that military supplies, equipment, and personnel were also crossing the border in support of militia groups in Sinai. The Egyptian army is engaged in a widespread military operation to regain control of Sinai from militant groups that have killed dozens of Egyptian policemen and soldiers.