Thousands of supporters of Egypt's Muslim Brotherhood stood their ground in Cairo today, saying they would not leave the streets despite "massacres" by security forces who shot dozens of them dead.

Egypt's ambulance service said 72 people were killed in yesterday's violence at a Cairo vigil by supporters of deposed President Mohammed Mursi.

The Muslim Brotherhood has vowed not to leave the streets unless Mr Mursi is restored to power.

His supporters accuse the military of reversing the uprising that brought democracy to the most populous Arab state.

"They will not be content until they bring back everything from the era of the corrupt, murderous security and intelligence state," senior Brotherhood official Essam el-Erian said on Facebook.

"They've stepped up their efforts to do so by committing massacres never before seen in Egyptian history."

Although Cairo was quiet this morning, violent clashes rattled the Suez Canal city of Port Said.

A 17-year-old youth was killed in fighting between the pro and anti-Mursi camps and a further 29 people injured.

The violence has deeply polarised Egypt, with its secular and liberal elite so far showing little sympathy for the Brotherhood.

The secular and liberal elite have no reservations about the return to power of a military that ruled for 60 years before the 2011 uprising.

However, in one of the first signs of doubt from within the interim cabinet installed after the military takeover, Deputy Prime Minister for Economic Affairs Ziad Bahaa El-Din said the government must not copy the "oppressive and exclusionary policies" of its foes.

Mr El-Din wrote on Facebook: "Our position must remain fixed on the need to provide legal guarantees not only for the members of the Brotherhood, but for every Egyptian citizen. Excessive force is not permitted."