A bomb exploded Monday near Egyptian troops demolishing houses along the border with the Gaza Strip, causing no casualties but prompting authorities to raise security alert levels in the area as Egypt clears a buffer zone to halt weapons smuggling, military officials said.

The border town of Rafah and its surrounding areas in the northern part of the Sinai Peninsula have been under a state of emergency for more than a week since an Oct. 24 militant assault killed 31 troops. It was the deadliest attack on Egyptian troops in recent times.

No one claimed responsibility for the bombing, but the Northern Sinai has become a stronghold of Islamic militants who have carried out scores of attacks in recent months, mainly targeting soldiers and police. […]