Syrian rights activists and residents say government troops have raided one town near the Lebanese border and surrounded another near the Iraqi frontier in an ongoing crackdown on opposition protests.

The activists and residents say Syrian soldiers entered the western town of Zabadani, bordering Lebanon, in armored vehicles early Sunday, detaining at least 70 people.

Elsewhere, residents and activists say Syrian security forces massed around the eastern town of Al-Boukamal on the Iraqi border Saturday, after opening fire on residents staging anti-government protests. They say at least one protester was killed. The activists say some Syrian troops refused to fire on protesters and defected to the opposition.

Syrian state news agency SANA says “terrorist gangs” killed three security personnel in Al-Boukamal on Saturday.

In another development, the son of a Syrian opposition figure and writer says authorities arrested his father in a raid on his home in the Damascus suburb of Qatana on Sunday. Sixty-one-year old dissident Ali Abdullah had been released in May as part of a government amnesty after spending four years in prison for supporting calls for democratic reforms.

Syrian President Bashar al-Assad has been trying to crush a four-month long uprising against his 11-year autocratic rule. Hundreds of Syrian opposition activists met in the Turkish city of Istanbul on Saturday to try to form a unified movement that can offer a democratic alternative to Mr. Assad's government.