CAIRO • Egypt faces the prospect of a surge in sectarian bloodshed after the Islamic State in Iraq and Syria (ISIS) claimed responsibility for the bombing of a Coptic cathedral in Cairo that killed 25 people on Sunday, reported the New York Times.

The group warned of more attacks to come.

As Christians gathered in churches on Tuesday to pay their respects to the victims, most of them women, ISIS said it had sent a suicide bomber to the chapel on the grounds of St Mark's Coptic Orthodox Cathedral, seat of the Egyptian Orthodox Church.

ISIS identified the bomber by his nom de guerre, Abu Abdallah al-Masri. The Egyptian authorities on Monday named the attacker as Mahmoud Shafik Mohamed Mostafa but said he had used a different alias. There was no immediate explanation for the discrepancy, said the New York Times.

According to the news site, a surveillance video made public by the authorities showed a figure, said to be Mostafa, entering the church, followed moments later by a blast.

It was the deadliest militant attack on Egyptian civilians in years, and the country's worst act of sectarian violence since another Islamist group bombed a Coptic church in Alexandria in 2011.

ISIS vowed to escalate its "war on polytheism" - a phrase that, in the Egyptian context, is a thinly veiled reference to Christianity.

The threat suggested that the group, which has been battling the Egyptian military in the Sinai Peninsula for years, planned to intensify its operations in Egypt's biggest cities, said the news site.

It was an embrace of sectarian violence on a scale rarely seen before in Egypt, with ISIS suggesting that it was prepared to single out Egyptian Christians much as it did minority Shi'ites in countries like Iraq and Syria.

That poses a new challenge for President Abdel-Fattah el-Sissi, who is already grappling with an economic crisis that has led to a slump in his popularity.

President Tony Tan Keng Yam and Prime Minister Lee Hsien Loong have written to Mr el-Sissi and Egyptian Prime Minister Sherif Ismail respectively, to convey their condolences over the bomb attack.

In his letter, Dr Tan said: "Singapore strongly condemns the bomb attack, and stands in solidarity with Egypt against all forms of extremism and terrorism."