The US issued a security warning against terrorist attacks on western schools in the Middle East, including one in Cairo's south district of Maadi.

The warning from the US State Department's Bureau of Diplomatic Security cited an "anonymous" post on a jihadist website, which it said "encouraged attacks against American and other international schools in the Middle East, including western teachers employed at these schools."

The message added that although any specific or credible threats against American schools or individuals are still unknown, the State Department is still working with US-affiliated schools to review their security situations.

The warning – directed mainly at US citizens in Saudi Arabia – advised US citizens to maintain high levels of security and situational awareness.

A number of websites, like the SITE monitoring service, compile jihadist threats online.

Egypt witnessed one of its worst terrorist attacks in recent times on Friday, with a car bombing of an army checkpoint in North Sinai killing 31 soldiers and injuring 30 others.

The country is currently battling a militant insurgency in North Sinai that has been present for the last decade but has increased drastically in the past year after the army's popularly-backed removal of president Mohamed Morsi in July 2013.

While the attacks have mainly targeted security personnel in the Sinai Peninsula, they have also spread to Cairo and surrounding cities, with citizens killed and injured in the violence as well.