Former Egyptian president Hosni Mubarak, who was overthrown in an uprising in 2011, will be released from jail within days after a prosecutor cleared him in a corruption case, his lawyer says.

Fareed El-Deeb has told Reuters news agency the judicial authorities had ordered Mubarak, 85, be released in one of the remaining corruption cases against him.

The only legal grounds for Mubarak's continued detention rests on another corruption case which will be cleared up later this week, Mr El-Deeb said.

"All we have left is a simple administrative procedure that should take no more than 48 hours," he said.

"He should be freed by the end of the week."

Without confirming that Mubarak would be freed, a judicial source told the news agency the former leader would spend another two weeks behind bars before judicial authorities made a final decision in the outstanding case against him.

Mubarak, along with his interior minister, was convicted and sentenced to life in prison last year for failing to stop the killing of protesters in the revolt that swept him from power.

He still faces a retrial in that case after appeals from the prosecution and defence, but this would not necessarily require him to stay in jail.

Mubarak still faces a retrial on charges of complicity in the murder of protesters during the 2011 revolt.

25 policemen killed

The security situation in the Sinai Peninsula has deteriorated since Mubarak was overthrown and has become significantly worse since the army ousted president Mohamed Morsi on July 3.

Militants killed 25 policemen on Monday in the deadliest attack of its kind in years, as Egypt struggles to deal with violent unrest sparked by Mr Morsi's removal.

Security in the northern Sinai region has been tightened since the attack on the policemen.

Pictures on social media from the scene appear to show the police were bound then killed execution style.

The photos could not be immediately verified.

Egyptian military, police and intelligence officers have launched a search for the suspected Islamist gunmen they say are responsible for the attack.

Medical and security sources say three policemen were left wounded after the grenade and machinegun ambush near the town of Rafah on the border with Israel.

A sniper also shot dead a policeman in the Sinai city of El Arish, the state news agency said, quoting a security source.

Egyptian politicians who back the coup that ousted Mr Morsi say the killings are proof the authorities are fighting a war on terror.

They continue to reject international concern about the large number of protesters killed by security forces over the past week.

Mounting insecurity in Sinai worries Egypt and also the United States because the desert peninsula lies next to Israel and the Palestinians' Hamas-ruled Gaza Strip, as well as the Suez Canal, one of the world's most important shipping arteries.

Morsi's detention extended for 15 days

Pressing an official drive against the Islamist movement, a prosecutor ordered Mr Morsi, held in an undisclosed location since his removal, should be detained for another 15 days in a new case of inciting violence, the state news agency MENA said.

The Brotherhood itself has responded with outrage after 37 Islamists died in government custody on Sunday in an incident it described as "murder".

The authorities said the men died of tear gas suffocation during a thwarted jailbreak.

"The murders show the violations and abuses that political detainees who oppose the July 3rd coup get subjected to," said the Brotherhood, which has called for an independent, non-Egyptian investigation into the incident.

Appeal to stop use of live ammunition against protesters.

Human Rights Watch has called on the Egyptian government Monday to stop using live ammunition against protesters, as it challenged the official death toll from day one of the ongoing crisis.

The New York-based human rights group says the large-scale use of live ammunition was not only unjustified, but also a failure to abide by international policing standards.

With the death toll mounting every day, it wants Egypt's military rulers to "urgently reverse" police instructions to use live ammunition to protect state buildings.

Such lethal force should be used "only when strictly necessary to protect life," said Human Rights Watch's acting Middle East director Joe Stork.

"This excessive and unjustified use of lethal force is the worst possible response to the very tense situation in Egypt today.

"Egypt's military rulers should rein in police forces to prevent the country from spiralling into further violence.

The military should not be encouraging police to use even more lethal force."

Investigating the August 14 crackdown on the Rabaa al-Adawiya protest camp that triggered the ongoing crisis, Human Rights Watch said the death toll "appears to be at least 377" - higher than the figure of 288 released by Egypt's health ministry.

Human Rights Watch cited "first-hand documentation" and interviews with health workers, as well as a list of fatalities from the Egyptian Center for Economic and Social Rights, as the source for its toll.

Reuters