Two military officials say an explosive device went off near Egyptian troops demolishing houses in a town on the border with the Gaza Strip where Egypt is clearing a buffer zone to halt weapons smuggling.

The strong blast on Monday in the border town of Rafah caused no casualties, the officials say, but prompted authorities to raise the security alert level.

Rafah and surrounding areas in the northern part of the Sinai Peninsula have been under a state of emergency for more than a week since 31 troops were killed in a militant assault.

No one claimed responsibility for the attack, but the region has emerged as a stronghold of Islamic militants, who have carried out scores of attacks in recent months mainly targeting soldiers and police.