Israel says the tunnels are being used to smuggle weapons into Gaza
The bodies have been recovered of three Palestinians who died when a smuggling tunnel under the border between Gaza and Egypt collapsed, medics have said.
Five others who were inside the tunnel, near the Rafah crossing, are missing.
Tunnels are used to bring fuel, weapons and other supplies into Gaza, which has been under an Israeli blockade since Hamas seized control in June 2007.
The Islamist group, Hamas, said Egypt was to blame because of its policy of destroying or gassing the structures.
Egypt has been attempting to close the tunnel network to prevent the smuggling of weapons into the coastal territory. It has been accused of not doing enough in the past by Israel.
Hamas spokesman Ehab al-Ghsain said that Egypt's methods of tackling the tunnels - using water and explosives to destroy them or filling them with gas - were dangerous.
He said the tunnels were a result of the blockade of Gaza, and that Egypt "shares the blame" for their existence because it had been co-operating with Israel in keeping the border closed.
Mr Ghsain said that the problem would be resolved if the Rafah crossing was re-opened, allowing people access to vital supplies.
"We understand the American and Israeli pressure on Egypt, but that does not justify the killing of people in such a manner," he said.
Egyptian security sources told the Reuters news agency that they had pumped gas into tunnels under the border in recent months before sealing them off.
They said the gas was not harmful and was used to prevent Palestinians from trying to re-enter the tunnels.
Since 2007, Israel has only allowed humanitarian and basic supplies into Gaza in response to rocket attacks by militants there. Aid agencies say the blockade has created a humanitarian crisis.
A truce between Palestinian militants and Israel has been in place in Gaza since June, although some rockets continue to be launched.