At least one person has been killed and about 12 people, mostly foreigners, injured in a bomb blast outside Egypt's historic Hussein mosque in Cairo, Egyptian police have said.

The person killed in Sunday's blast in the popular tourist area was confirmed as a French woman.

Passersby were injured after being hit by stone and marble fragments after the bomb went off outside the mosque, a police official at the scene said.

French and German nationals were among the wounded.

"It was an explosive, perhaps a hand grenade," one police official said.

Blood stains could be seen in the front courtyard of the mosque, next to the famed Khan el-Khalili bazaar.

A second device was detonated without causing any injuries.

Blast investigated

Riot police cordoned off the area and sniffer dogs could be seen as worshippers were being evacuated from the mosque.

It was not clear who was behind the attack or if tourists had been deliberately targeted.

"Investigations are at a preliminary stage at the moment," Amr el-Kahky, Al Jazeera's correspondent in Cairo, said.

"It is very difficult to speculate whether foreigners were the target of this attack.

"All the Islamic groups that were operating and were violent in the nineties [in Egypt] have issued an initiative in which they declared a unilateral ceasefire against the Egyptian government."

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