By Ahmed Aboulenein and Eric Knecht

CAIRO (Reuters) - Hundreds of Egyptian protesters angered by President Abdel Fattah al-Sisi's decision to hand over two islands to Saudi Arabia called on Friday for the downfall of the government, chanting a powerful slogan used in a 2011 uprising.

Sisi, who once enjoyed widespread support, has faced mounting criticism in recent months over a range of issues, including his management of the economy.

The protesters also chanted: "Sisi Mubarak", "We don't want you, leave" and "We own the land and you are agents who sold our land."

In other parts of Cairo, police fired tear gas at protesters, security sources said.

A Reuters witness said a crowd was dispersed and riot police had taken control of an area outside a mosque in the Mohandiseen district of the capital. Four people were arrested, the security sources said.

Sirens could be heard across the area. A police armoured truck carrying security forces conscripts drove past.

Tear gas was also fired in the Giza area outside Cairo, dispersing about 200 people, security sources said.

Sisi's government announced last week the signing of a maritime demarcation accord that puts uninhabited Red Sea islands in Saudi waters, prompting an outcry in Egyptian media.

Critics say the government has mishandled a series of crises from an investigation into the killing of an Italian student in Cairo to a bomb that brought down a Russian airliner in the Sinai last October.

Many Egyptians, eager for stability after the turmoil triggered by the 2011 uprising against Mubarak, enthusiastically welcomed Sisi when he seized power from the Muslim Brotherhood in 2013 after mass protests.

But the former army general no longer enjoys the cult-like adulation of his early days in power.

Egypt's interior ministry said on Thursday it would take legal action against people who participate in demonstrations called by activists to protest against the transfer of the islands, Tiran and Sanafir.

Saudi and Egyptian officials say the islands belong to the kingdom and were only underEgyptian control because Saudi Arabia had asked Cairo in 1950 to protect them.

On Wednesday, Sisi tried to calm the furore, reiterating the government's line that the islands had always been Saudi and that Egypt had only been looking after them.

Calls for protests have gathered thousands of supporters on Facebook, including from the outlawed Muslim Brotherhood.

(Writing by Michael Georgy