Egypt's most active militant group, Ansar Bayt al-Maqdis, has sworn allegiance to Islamic State, the al Qaeda offshoot which has seized territory in Syria and Iraq, according to an audio clip posted on its Twitter account.

If genuine, the declaration of allegiance would be a boost for Islamic State, showing its widening influence in the region alongside its territorial advances in Iraq and Syria.

The Sinai-based militant group posted the clip, which is 9 minutes and 26 seconds in length, early on Tuesday morning on a Twitter account that calls itself the official mouthpiece of Ansar.

The clip was then carried on a website used by Islamists.

Reuters was not immediately able to verify the authenticity of the statement nor contact the group directly for comment.

In the clip, a man identifies himself only as part of the group's "information department". He says the militants had pledged loyalty to Abu Bakr al-Baghdadi, head of Islamic State, which is now facing U.S.-led air strikes.

The Twitter account has issued other statements on the group's behalf in recent months. It is often suspended and re-opened; one of these shutdowns occurred hours before the statement was tweeted.

The posting comes the week after the group distanced itself from a statement pledging loyalty to Baghdadi that appeared in its name online and was reported by Reuters.

Egyptian security officials have said Islamic State has established contacts with Ansar Bayt al-Maqdis, though the precise nature of these to date is unclear.

In September, Islamic State issued a statement urging insurgents in Sinai to push ahead with attacks on the country's security forces.

Egyptian President Abdelfattah al-Sisi has said Egypt faces an "existential threat" from Sinai-based militants who have killed hundreds of police and soldiers since the army ousted Islamist President Mohamed Mursi last year.

Last month, at least 33 security personnel were killed in two successive attacks, prompting Egypt to declare a three-month state of emergency in parts of northern Sinai.

The attacks were a setback for the government, which had managed over the past few months to make some progress in the struggle against insurgents and focus on repairing the economy.

(Reuters)