Egyptian ex-President Hosni Mubarak, in detention pending a probe into state violence against protesters, was reported on Thursday to be in "stable" condition after suffering a heart attack.

The official MENA news agency in a brief statement said the 82-year-old former strongman's condition was "stable and reassuring."

Egyptian protesters who spearheaded a popular uprising that toppled Mubarak in February, hailed his detention and that of his two sons as a "positive step" by the Army.

All three were placed under 15 days detention on Wednesday, with Mubarak incarcerated in hospital in the Red Sea resort of Sharm el-Sheikh after suffering a heart attack during interrogation by prosecutors the previous day.

His two sons, Gamal and Alaa, are being held in Cairo's Tora prison complex, home to other fallen officials and some of the country's most notorious political prisoners.

Chief prosecutor Abdel Maguid Mahmud authorised the detention for 15 days "as part of an inquiry into the use of force against protesters during the unrest in January and February," an official statement said.

Long time Mubarak ally the United States remained mum on the move, saying it was an internal Egyptian matter.

The youth group that spearheaded the protests that toppled Mubarak and has since pressed for his trial, was elated and said it would suspend a demonstration planned for Friday.

"This is a positive step, and we hope it is followed by the release of protesters arrested during the revolution and after," said Shadi Ghazali Harb, an organiser with the Youth of the January 25 revolution group.

"We've suspended the planned protest for Friday; this was a main demand and the first step has been achieved," he said.

Mubarak resigned on February 11 after 18 days of protests, with security forces believed to have killed hundreds of people in the first few days.

He and his sons were to be asked about allegations that they were "connected to the crimes of assault against protesters, leading to deaths and injuries", the official news agency MENA said.

Al-Ahram newspaper Thursday reported, "great popular joy" at the decision to detain Mubarak and his sons.

It quoted the Supreme Council of the Armed Forces, which assumed control after Mubarak resigned, as saying that "no one is above the law."

According to independent daily Al-Masri Al-Yom, which said it had obtained information about Mubarak's interrogation, the former strongman has denied ever giving an order for protesters to be attacked.

Mubarak told his Interrogators, it added, that he had ordered his security forces into the streets "to protect and reassure the population."

Mubarak's supporters, who have held occasional apologetic demonstrations since the president's ouster, announced on Facebook calls for a sit-in until his release.

They appealed to "all those who respect religion, law and human rights to save a man who spent 62 years of his life in service of the country."

On Wednesday, MENA said the 82-year-old Mubarak was in "unstable" condition and under observation but later in the day the doctor tasked by prosecutors with assessing Mubarak's health said his condition had improved.

The Mubaraks are accused of incitement to fire at demonstrators during the popular uprising that broke out on January 25. Nearly 800 people died during the uprising.

The inquiry was launched after the broadcast of an audio tape in which Mubarak defended his reputation and after weeks of mounting protests calling for him to be tried.