By Asma Alsharif and Tom Perry
CAIRO (Reuters) - Nine people were killed in Cairo on Tuesday in clashes between opponents and Islamist supporters of Egypt's deposed President Mohamed Mursi, state-run media reported, keeping the most populous Arab nation in turmoil.
The violence broke out before dawn near a Brotherhood protest at Cairo University, where Mursi supporters have been camped out since the army removed the Islamist politician from power on July 3 following protests against his rule.
The Brotherhood described it as an attack on peaceful protesters and blamed the killing on thugs backed by the Interior Ministry - an accusation a security official denied.
Police sources said hundreds of Mursi supporters clashed with local residents, street vendors and others near the sit-in. They said gunshots were fired and stones were thrown.
With the Brotherhood vowing to stay in the streets, the bloodshed was a fresh example of the instability facing Egypt as the newly installed interim government moves along an army-backed roadmap towards elections in about six months.
"The longer this standoff continues, the more hardened the positions become, and the more likelihood there is for violence, and oppression," said Yasser el-Shimy, Egypt analyst with the International Crisis Group.
"It needs an urgent political deal or compromise and unfortunately we are not seeing any signs of that."
The state-run Al-Ahram newspaper quoted a health ministry official as saying nine people had been killed and 33 wounded in the Cairo University clashes, while two wounded in fighting on Monday had died, bringing to 14 the number of deaths in violence between rival protesters in Egypt in the last two days.
At least 15 burned-out cars lay abandoned around the university area where the clashes took place. Splattered blood and broken glass disfigured the pavements near the shopping area where a traffic police station was set on fire.
Brotherhood members with sticks guarded the entrance to the protest site after the clashes calmed, while residents stopped cars on the road to Cairo University to check for weapons.
About 100 people have died in violence since the army deposed Mursi and replaced him with an interim administration led by the Adli Mansour, the head of the constitutional court. The Brotherhood accuses the army of orchestrating a coup.
It said on its website that seven "martyrs" had been killed overnight in two separate attacks on Mursi supporters, one at Cairo University and another during a march near a bigger round-the-clock sit-in in the north of the city.
Egypt's general prosecutor ordered 22 pro-Mursi protesters be detained for 15 days while they are investigated over accusations they attacked the ousted president's opponents in central Cairo on Monday, the state news agency said.
They are also accused of carrying unlicensed fire arms and ammunition, the report said.
BROTHERHOOD PROTESTERS "TERRORISED"
The Brotherhood vows to keep up its vigil until Mursi, 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 terrorize the peaceful protesters in Egypt," the Brotherhood's Freedom and Justice Party said in a statement.
Mursi'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 Mursi's release and an end to "all politicized 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 Mursi'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 Mursi's overthrow on July 3.
Israel has boosted its rocket defenses 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 Defense Minister Moshe Yaalon said. "We have indeed strengthened our deployment along the border." [ID:nL6N0FT1ZN]
(Additional reporting by Yasmine Saleh and Ahmed Tolba in Cairo and Maayan Lubell and Dan Williams in Jerusalem; Editing by Alistair Lyon and Michael Roddy)