WASHINGTON (AFP) - The United States on Tuesday denounced violence in Egypt that left seven people dead after security forces clashed with supporters of the country's ousted president Mohamed Mursi.

State Department spokesman Patrick Ventrell was careful to note that Washington was not taking sides in the turmoil, after the Egyptian army toppled the elected Islamist leader on July 3 amid mass protests.

"We... strongly condemn the overnight violence in Cairo," Mr Ventrell told reporters. "Simply put, violence makes the transition much more difficult."

Clashes on the streets of Cairo and in nearby Giza, which left more than 260 wounded, came only hours after US Undersecretary of State Bill Burns visited the country and appealed for an end to violence.

"We don't take sides" and Washington wants to see Egypt "get the democratic process back on track", Mr Ventrell said.

The spokesman said the message Mr Burns had conveyed in Cairo was Washington's "desire to have an inclusive, tolerant, democratic future for Egypt".

"He talked about our desire for a non-violent, inclusive path forward," he said.

Although Mr Burns did not have a face-to-face meeting with Mr Mursi's Muslim Brotherhood movement, the US diplomat did speak by phone to one of the group's representatives, Mr Ventrell said.

"We want to ease the polarisation that can poison society - we want to move from polarisation," he said.

Egypt has been shaken by a series of deadly attacks since the coup, and the latest deaths brings to more than 100 the number of people killed, according to an AFP tally of confirmed deaths.