CAIRO (AFP) - A new Egyptian Islamist group claimed responsibility for a spate of attacks on policemen in the Nile Delta that marked an escalation of a militant campaign following Islamist president Mohamed Morsi's overthrow.

Ansar al-Shariah, a name used by jihadist groups in other countries, had recently announced its formation in Egypt, before issuing another statement on Monday saying it targeted 28 "treasonous" security men.

More than 200 policemen and soldiers have been killed by militants based in the restive Sinai Peninsula since the army overthrew Morsi in July.

Militants have spread their reach to the capital and the Nile Delta, carrying out car bomb and shooting attacks against police targets.

The statement, posted on Facebook and circulated on militant Islamist forums, said the attacks in the Nile Delta over the past few months were to avenge abuses against "our sisters," a possible reference to detained Islamist women.

The statement's authenticity could not be verified.

Most of the attacks have taken place in the Nile Delta province of Sharqiya, where many policemen have been shot dead since January.

The group spearheading the attacks, Ansar Beit al-Maqdis, is believed to be led by hardline Bedouin militants in the Sinai.

It has claimed responsibility for bombings of police headquarters in Cairo and elsewhere, and for the downing of a military helicopter in the Sinai using a heat-seeking missile.