The family of ousted Egyptian President Mohammed Mursi has said it will take legal action against the army, accusing it of abducting the country's first democratically-elected president.

Mr Mursi has been held at an undisclosed military facility since the army removed him from office on 3 July.

It suspended the constitution in the wake of huge street protests against his one-year rule.

The army says Mr Mursi is being held for his own safety.

"There is no legal or constitutional basis ... for detaining someone not accused of a crime for his own safety," Mr Mursi's son, Osama, told a news conference marking the family's first formal appearance since his removal.

He said the family would take immediate legal action "inside Egypt and at an international level" against Abdel Fattah al-Sisi, the army commander and defence minister who played a central role in forcing Mr Mursi from office.

Osama said the family had not been in touch with their father since his removal and had no information on the state of his health.

Mr Mursi's Muslim Brotherhood accuses the army of orchestrating a military coup.

It denounced a move, launched yesterday, to revise Egypt's constitution, drafted last year by an Islamist-dominated body and adopted despite objections from Christians and liberals.

The Brotherhood calls the military-backed interim government illegitimate.

"[Mursi's] arrest and that of his advisors is completely illegal," said Heba Morayef, Egypt director of Human Rights Watch.

Under international law, she said, the maximum time someone can be held without charge is 48 hours.

Meanwhile, six people were killed and 11 others wounded in several attacks by militants in the Sinai peninsula, near Egypt's borders with Israel and Gaza, medical sources said.

Two civilians, two army officers and two policemen were killed in at least ten attacks in the province's main northern cities of Rafah and El-Arish overnight against police stations and security and army checkpoints, according to the sources.

The latest violence there was the worst so far this month in terms of the number of attacks and victims in a single day.