(Reuters) - Canada's Embassy in Cairo was closed on Monday until further notice because of security concerns, an official answering its emergency telephone line said, the second diplomatic mission to shut its doors this week.

A message on the embassy's website read: "The ability to provide consular services may occasionally be limited for short periods due to unsettled security conditions." It gave no more details.

The British Embassy in Cairo closed to the public on Sunday, also citing security concerns. A notice on its website on Monday said its services remained suspended.

Egypt is battling an Islamist insurgency largely centered around Sinai, a strategic area near the border with Israel, Gaza and the Suez Canal.

Insurgent attacks have mostly targeted Egyptian police and soldiers, killing hundreds in the past year, but Egypt's most dangerous militant group, Sinai Province, said on Monday it was behind the killing of an American oil engineer in the western desert in August.

Smaller bombs also regularly explode in Cairo and the Nile Delta, usually causing limited injuries.

One security source told Reuters on Sunday it was not yet clear what threats had prompted the British embassy to close its doors.

But another source, who spoke on condition of anonymity, said a suspected militant who was recently detained by Egyptian authorities had confessed to plans to target foreign embassies.