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By Yasmine Saleh and Tom Finn
CAIRO, Aug 14 (Reuters) - Egyptian security forces killed at least 30 people on Wednesday clearing a camp of Cairo protesters who were demanding the reinstatement of deposed President Mohamed Mursi, his Muslim Brotherhood movement said.
The move, around 7 a.m., came after international efforts failed to mediate an end to a six-week political standoff between Mursi's supporters and the army-backed government which took power after his ouster on July 3.
With the Brotherhood calling on its supporters to take to the streets, the violence risked further destabilising a pivotal Arab nation and endangering hopes for democratic government.
There was no official confirmation of the deaths at Rabaa al-Adawiya, in northeast Cairo where thousands of Mursi supporters awoke to police helicopters circling the site. A second camp at Nahda was swiftly cleared in the early morning.
Clouds of black smoke could be seen rising above the camps. Gunfire was heard as protesters ran away from Rabaa where bulldozers were used to clear tents and where one witness said he saw 15 bodies at a field hospital.
"It is nasty inside, they are destroying our tents. We can't breath inside and many people are in hospital," Murad Ahmed said at the edge of the sprawling camp, where Muslim Brotherhood guards had positioned sandbags in anticipation of a police raid.
Two members of the Egyptian security forces were shot dead as they tried to disperse protesters, the state news agency reported.
The break up of the camps would strip the Brotherhood of its main leverage against the government. The group's leaders have been arrested or are wanted and their assets frozen in one of the toughest crackdowns it has ever faced.
Television pictures showed security forces shooting from the roofs and protesters reported clouds of tear gas.
"Tear gas was falling from the sky like rain. There are no ambulances inside. They closed every entrance," said protester Khaled Ahmed, 20, a university student wearing a hard hat with tears streaming down his face.
"There are women and children in there. God help them. This is a siege, a military attack on a civilian protest camp."
The state news agency said security forces had started implementing a phased plan to disperse the protesters, which is almost certain to deepen political turmoil in Egypt.
Egypt has been convulsed by political and economic turmoil since the 2011 uprising that ended 30 years of autocratic rule by U.S.-backed President Hosni Mubarak, and the most populous Arab nation is now more polarised than any time for many years.
There is deepening alarm in the West over the course taken by Egypt, which sits astride the Suez Canal and receives $1.5 billion a year in mainly military aid from the United States.
More than 300 people have already died in political violence since the army overthrew Mursi on July 3, including dozens of his supporters killed by security forces in two separate earlier incidents.
Mursi became Egypt's first freely elected leader in June 2012 but failed to tackle deep economic malaise and worried many Egyptians with his apparent efforts to tighten Islamist rule. (Writing by Michael Georgy; Editing by Anna Willard)