Witnesses say several thousand Syrian army troops, flanked by special forces, shot their way into the southern city of Daraa before dawn Monday, causing numerous casualties. Tanks reportedly began the assault, shelling the city as they moved in from four sides.
Videos distributed by human rights activists show black smoke over the city center and fires burning as shell-fire crackled in the background.
Reports say Syrian special forces stormed private homes to make arrests, Witnesses say snipers began shooting from rooftops and many victims remain lying in the streets.
Jordanian authorities said the main highway crossing between Jordan and Syria was closed to traffic and that two border posts were not allowing anyone to enter Syria.
Syrian rights activists say that security forces also encircled the Damascus suburbs of Douma and Madaamiya, arresting hundreds of people.
The crackdown came as Syrian government media condemned what was called the "crimes of armed gangs" and "outside plots to divide the country." Syrian television reported that 15 members of the army and security forces were killed in recent violence.
The sister of one such victim said on state television she was proud that her brother had died to defend his country.
She says she is the sister of martyr Nihad Ayoub, and while she is sad her brother died, she thanks God for his sacrifice.
The Syrian government daily Tishreen condemned what it called "outside media mobilization campaigns" against Syria, complaining that "freedom cannot be exercised amid chaos....without security for the country and its citizens."
But Nadim Houry of Human Rights Watch in Beirut called on the United Nations to begin an independent international investigation into what he said are "abuses that have occurred in Syria in the past five weeks."
He also urged the European Union and the United States to impose sanctions on the Syrian leadership, a move the Obama administration said it is considering.
The U.N.’s top human rights official, Navi Pillay, demanded that Syria curtail its crackdown and urged a "full and independent investigation" into the killings of protesters.