TRIPOLI, Libya — Moammar Gadhafi loyalists broke through rebel lines at an opposition-held city that is closest to the Libyan capital today, while anti-government forces celebrated the capture of a key oil port from the regime on the eastern coast.

The contrasting fortunes of the two warring sides suggest that the conflict in Libya is veering toward a lengthy civil war, with the government fighting fiercely to maintain its hold in Tripoli and surrounding areas and the rebels pushing their front westward from their eastern stronghold.

Gadhafi, who has led the country virtually unchecked for four decades, has unleashed a violent crackdown against those seeking his ouster, drawing international condemnation and sanctions.

Hundreds have been killed, perhaps more, putting pressure on the international community to do more to stop the crackdown on protests that began on Feb. 15, inspired by successful uprisings in Egypt and Tunisia, its neighbors to the east and west respectively.