BROTHERHOOD PROTESTERS "TERRORISED"

The Brotherhood vows to keep up its vigil until Morsi, held in an unknown location since the army ended his year in power as Egypt's first freely elected president, is reinstated.

"Leaders of the military coup continue to terrorise the peaceful protesters in Egypt," the Brotherhood's Freedom and Justice Party said in a statement.

Morsi's family said on Monday it would sue the army for holding him without charge. The United States, which gives Egypt $1.3 billion a year in military aid, has called for Morsi's release and an end to "all politicised arrests and detentions".

Some residents near the Islamist movement's main protest area in Nasr City have filed a complaint with the public prosecutor asking for the removal of the protesters. A security source said on Tuesday a court was expected to rule on the case soon "to give the army a legal basis to end the protests".

The National Salvation Front, an alliance of liberal and leftist parties that supported Morsi's ouster, condemned what it described as attacks by Brotherhood supporters on protesters over the last three weeks.

In separate overnight clashes, a civilian and a policeman were killed in the lawless North Sinai region, near Egypt's borders with Israel and the Palestinian Gaza strip, where hardline Islamists have stepped up attacks on security forces.

A security vacuum following the 2011 uprising that ousted President Hosni Mubarak resulted in a surge of attacks in North Sinai. At least 20 people have been killed in militant violence there since Morsi's overthrow on July 3.

Israel has boosted its rocket defences near its southern border with Egypt to counter possible attacks from Islamist militants there, Israeli officials said on Tuesday.

"We hear reports every day of attacks there and our concern is that the guns will be turned on us," Israeli Defence Minister Moshe Yaalon said. "We have indeed strengthened our deployment along the border."