Updated

Syrian authorities pursuing a crackdown against President Bashar Assad's critics banned three prominent opposition figures from leaving the country Sunday, and security forces killed two people and arrested several others in northern Syria, activists said.

Michel Kilo, Loay Hussein and Fayez Sara were on their way to neighboring Lebanon to take part in a televised panel discussion when they were told by Syrian immigration authorities at the border that they were prohibited from leaving out of concern for their safety in Lebanon.

Hussein denounced what he called an attempt to keep them from speaking on television. The debate was to be aired by the U.S.-funded Al-Hurra television.

"This decision negates all talk about transparency and reforms," said Sara. "It is unjustified and illegal," he added.

In northern Syria, security forces killed two people and detained scores of others during raids and house-to-house arrests in the Khan Sheikon village.

The Local Coordination Committees activist network and the London-based Syrian Observatory for Human Rights confirmed the deaths. They said similar arrests were made in the eastern Deir el-Zour and reported intermittent gunfire that erupted in several areas across the country.

Snipers shot dead one man in the Damascus suburb of Saqba overnight after troops deployed in the restive area, they said.

Syria's Interior Ministry urged residents of the capital not to respond to calls posted on social media networks to stage protests in Damascus squares "for their own safety" after some of the most intense protests there since the start of the five-month uprising against Assad.

Human rights groups say Assad's forces have killed more than 2,000 people since the uprising erupted in March, touched off by the wave of revolts sweeping the Arab world.

Central Damascus has been largely quiet in comparison with other major cities. On Saturday, Syrian forces fanned out in the capital and its suburbs to prevent protesters from converging on the center of Damascus.

Activists said security forces fired live ammunition and beat up protesters emerging from the al-Rifai mosque in the Kfar Sousa district of the capital Saturday after they tried to stage a protest, wounding several. They included the mosque's preacher, Osama al-Rifai.

The attack triggered sit-ins and protests in several other parts of the capital and its suburbs Saturday and overnight.

Intense protests in Damascus and Aleppo, Syria's two largest cities and economic powerhouses, would pose a real threat to Assad.

Assad has met the extraordinary revolt against his family's 40-year dynasty with a brutal security crackdown, but has also acknowledged the need for reform. He has lifted decades-old state of emergency laws and this month endorsed new laws that would allow the formation of political parties alongside the ruling Baath party and enable newly formed political parties to run for parliament and local councils.

On Sunday, he endorsed a new media law that would restrict government censorship of local and foreign publications and end government control over the media.

The opposition dismisses those changes, once key demands, as too little too late.

The uprising has left Assad with few international allies -- with the vital exception of Iran, which the U.S. and other nations say is helping drive the deadly crackdown on dissent.

Iran said Saturday that a power vacuum in Damascus could spark an unprecedented regional crisis while urging Assad to listen to some of his people's "legitimate demands."

In an emergency meeting on Syria that ended early Sunday in Cairo, the Arab League decided to send its leader, Nabil Elaraby, to Damascus to seek a solution. In a statement, the league expressed "grave concern" over the bloodshed in Syria.