Security forces killed at least 15 people and arrested more than 200 people in Syria, activists said, as Human Rights Watch denounced on Saturday a "deliberate policy" to disperse protesters with deadly force.

The deaths came as Damascus accused the U.S. envoy of inciting violence in Hama -- where nearly half a million people protested on Friday -- a charge roundly denied by Washington which accused the Syrian embassy of spying on demonstrators in the United States.

Hundreds of protesters spent the night in Cairo's Tahrir Square, an Agence France Presse reporter said on Saturday, after mass nationwide rallies to press the new military rulers to make good on promises of reform.

Dozens of tents were pitched in the square -- the focus of protests that ousted veteran president Hosni Mubarak in February -- and traffic was blocked around the usually busy plaza where music blasted from loudspeakers.

Washington summoned the Syrian ambassador for talks this week after reports that embassy staff had filmed U.S. protests against the crackdown in Syria, the State Department said Friday.

Ambassador Imad Mustapha was called in to meet with top State Department officials "to express a number of our concerns with the reported actions of certain Syrian embassy staff in the United States," the agency said.

Embattled Libyan leader Moammar Gadhafi said in an audio message relayed to supporters on Friday that his regime will not fall and told NATO to stop attacking his troops.

"The regime in Libya will not fall -- it is based on the people, not on Gadhafi. NATO is wrong if it thinks it can topple the regime of this country," he said in the message to thousands of supporters in Sabha, some 750 kilometers south of Tripoli.

Fearing an acute shortage of medical and other essential supplies, Libya's rival factions are in talks with the United Nations to ease international sanctions on the war-torn nation, Agence France Presse has learned.

Well-placed U.N. officials said representatives from Libya's rebel council and Moammar Gadhafi's regime held talks last week with the World Health Organization aimed at drawing up a list of items for sanctions relief.

Tens of thousands rallied in Sanaa on Friday to "reject" Yemen's dependence on the United States and Saudi Arabia, saying badly burned President Ali Abdullah Saleh was "politically dead" after a TV appearance.

Meanwhile, thousands of Saleh supporters staged a rival rally in the capital's southern district on what they have named "The Friday of thanks" over Saleh's health, chanting "The people want Ali Abdullah Saleh."

At least 13 Syrian protesters were killed and 40 others wounded on Friday across the country as nearly half a million people demonstrated in the protest hub of Hama, activists said.

Rami Abdul Rahman, chief of the Syrian Observatory for Human Rights, said that at least 450,000 Syrians rallied after Friday prayers in Hama under the banner "No to dialogue" with President Bashar al-Assad's regime.

Both the U.S. and French ambassadors to Syria were in the protest hub of Hama on Friday to observe anti-regime rallies there as nearly half a million people demonstrated in the flashpoint central city.

The move prompted the Syrian government to accuse the U.S. ambassador to Damascus, Robert Ford, of meeting "saboteurs" in Hama and inciting protests against President Bashar al-Assad.

Thousands of people took to the streets across Egypt on Friday to defend the uprising that toppled president Hosni Mubarak, directing their anger at the new military rulers over the slow pace of reform.

Flag-waving protesters converged on Cairo's Tahrir square to push for democratic change and demand that former regime officials accused of abuse be brought to justice.

Scores of pro-Palestinian protesters trying to reach Israel were blocked at airports in Europe and two American activists who arrived in Israel were deported early Friday, Israeli officials said.

Israel increased security at the Ben-Gurion International Airport ahead of the activists' arrival and asked foreign airlines to prevent blacklisted travelers from boarding Israel-bound flights, as hundreds said they would travel to Israel to protest Israeli policies toward the Palestinians.