Top US diplomat Hillary Clinton called on Egyptians to refrain from violence after a third straight day of deadly clashes in Cairo.

"I urge Egyptian security forces to respect and protect the universal rights of all Egyptians, including the rights to peaceful free expression and assembly," a "deeply concerned" Clinton said in a statement yesterday.

At least 10 people were killed in the latest unrest in the Egyptian capital, overshadowing the count in the first post-revolution vote that shows Islamists in the lead. A historic library housing priceless archives was also destroyed.

"We call upon the Egyptian authorities to hold accountable those, including security forces, who violate these standards," Clinton said, expressing condolences for the families of those killed or injured.

"Those who are protesting should do so peacefully and refrain from acts of violence."

In central Cairo, armed forces detained over 180 people including minors, the prosecutor's office said, as street battles raged outside parliament and government offices where protesters are demanding an end to military rule.

The clashes were the deadliest in weeks and have sparked a furious debate over the army's role during the transition. The violence marred the count in the second round of a multi-stage election that saw a 67 percent turnout and in which the largest Islamist parties claimed victory.

The Muslim Brotherhood's Freedom and Justice party (FJP) said it won 39 per cent of votes in the party lists, while the Al-Nur party, which represents the more hardline brand of Salafi Islam, claimed more than 30 per cent of votes in the lists. 

Tags: Egypt unrest, Egyptian violence, Hillary Clinton