At least 24 people have been reported killed and others injured in fighting in the Egyptian capital of Cairo.

The violence broke out after a protest in Cairo against an attack on a church in Aswan province last week, which Coptic Christians blame on Muslim radicals.

The Foreign & Commonwealth Office has not altered its travel advice to the country but warned travellers to avoid the area around Tahir Square and stay away from all demonstrations.

There has also been disruption to flights at Cairo airport with unconfirmed reports pointing to an air traffic control dispute which has now ended, according to the FCO. “Flights are now operating again although with some delays and cancellations,” it said.

As Egyptian prime minister Essam Sharaf called for calm in the capital, the FCO confirmed that people had been killed and large numbers of others injured in the Mispero area of downtown Cairo. “Please stay away from this area and the area around Tahir Square,” the FCO said. “Please avoid all demonstrations.”

Sharaf said discord between Muslims and Christians in Egypt was “a threat to the country’s security”.

Speaking on television after touring the area where the clashes had occurred late on Sunday, Sharaf said: “The most serious threat to the country’s security is tampering with national unity, and the stirring of discord between Muslim and Christian sons of Egypt.”

He added that such violence – the worst in Egypt since President Hosni Mubarak was ousted in February – was also “tampering with the relationship between the people and the army”. A night-time curfew is in force in parts of Cairo until 7am local time.