A policeman was killed as he tried to defuse a bomb near a church in Cairo, Egyptian authorities said

The blast also wounded the commander of the bomb squad and another officer, according to the country's interior ministry.

The device was in a suitcase hidden of the rooftop of a building close to the church in the Nasr City suburb of the capital, the ministry added.

The blast came just two days before the Orthodox Coptic Church, the dominant denomination among Egypt's estimated 10 million Christians, celebrates Christmas.

It also came a little more than a week after a roadside bomb hit a tourist bus near the Giza Pyramids, killing three Vietnamese tourists and their Egyptian driver.

Saturday's incident will likely spur authorities to further tighten security around churches ahead of the Coptic Orthodox Christmas on Sunday.

Armed policemen guard churches, and security guards check the identity of visitors. Metal detectors have also been set up outside churches.

The heightened security followed a spate of attacks claimed by Isis that has targeted churches and buses carrying pilgrims to remote desert monasteries, killing more than 100 Christians over the past few years.

As was the case last year, the Coptic Christmas mass is expected to be held at a new cathedral in Egypt's new administrative capital that is being built east of Cairo.

Attack on Christians in Egypt kills 7, Egyptian State TV reports

No one immediately claimed responsibility for Saturday's blast, which bore the hallmarks of Isis, which spearheads an insurgency centred in the northern region of the Sinai Peninsula.

Egypt has been battling Islamic militants for years, with the army and police now engaged in an all-out campaign to eradicate them, throwing into battle tens of thousands of troops backed by fighter jets, helicopter gunships and warships.