CAIRO (REUTERS) - Muslim Brotherhood supporters and police clashed across Egypt on Friday, leaving at least two dead in protests after the army-backed government declared the group a terrorist organisation.

Violence flared after Friday prayers.

An 18-year-old Brotherhood supporter was shot dead during clashes in the Nile Delta city of Damietta, police said.

Another man was killed in Minya, a bastion of Islamist support south of Cairo.

Meanwhile, security forces detained nearly 150 Brotherhood supporters in a new wave of arrests.

The widening crackdown has increased tensions in a country rocked by the worst internal strife of its modern history since the army deposed Islamist President Mohamed Mursi in July.

Security forces have killed hundreds of his supporters, and lethal attacks on soldiers and police have become commonplace.

The Brotherhood was declared a terrorist organisation after 16 people were killed in a suicide attack on a police station on Tuesday, although the group condemned the attack and it was claimed by a radical faction based in the Sinai Peninsula.

The Muslim Brotherhood and its Islamist allies had called for protests in response to the government decision.

Clashes between police and protesters flared in Cairo and at least four other cities of Friday.