On Friday, clashes between pro-democracy protesters and security forces across Syria resulted in the bloodiest day in the country's five-week-old uprising. This morning, it looks like Syria could be headed toward another day of deadly confrontations. Bashar al-Assad's regime has launched what Al Jazeera is calling an "unprecedented" offensive in the southern city of Daraa (where unrest first erupted in mid-March), the Damascus suburb of Douma, and the coastal town of Jableh. Troops, tanks, and snipers entered Daraa at dawn, according to witnesses, and at least five people were killed when gunmen shot at a car. 

Today's developments mark the first time that the military has become directly involved in the uprising, Al Jazeera's Rula Amin explains, and the first time that security forces are sweeping cities in the absence of demonstrations, with reports of house-to-house searches, arrests, and "random shooting." In another sign of an escalated crackdown, Reuters is reporting that Syria has closed all border crossings on its southern frontier with Jordan.

Yet even as the regime flexes its muscle, there are also signs that its violent tactics are undermining some of its support. An activist tells Al Jazeera that some army officers have defected in Daraa a day after two Syrian lawmakers resigned, and news outlets are reporting that the Obama administration is considering sanctions against Syrian officials, which might pressure European countries to follow suit.

Overnight, the Sham news agency has posted videos allegedly showing tanks entering Daraa. In this first video, protesters throw rocks at a tank:

Another video shows a tank entering the city amid gunfire: