The offensive started on the city of Homs, where neighborhoods that have seen some of the largest protests and armed resistance to the government are now under constant fire from tanks, rockets and mortars.
Homs is in central Syria, and it is thought that if the regime lost it to the opposition, that would cut the country in half. The offensive continued in the city of Zabadani, a mountain resort town just outside of Syria's capital of Damascus.
Now that the uprising in Syria has turned into a heavily armed conflict, many in the region are worried that the violence will spread beyond its territory.
Syria borders Iraq, Turkey, Jordan and Israel, as well as Lebanon, where clashes erupted last Friday in the northern coastal city of Tripoli.
Sunni Muslims in one Tripoli neighborhood began protesting against Syrian President Bashar Assad. They put up a huge banner on the side of a mosque that had a picture of Assad, wearing a military uniform, with a big red X across his face.