TRIPOLI, Sept. 20 (Xinhua) -- Violent clashes resumed in Libyan capital Tripoli after the ceasefire agreement continued to be violated for the second day in a row.

"The clashes have been renewed since the mid-day in all areas of south and southeast of Tripoli between government forces and the Seventh Brigade," an Interior Ministry source told Xinhua late on Wednesday.

"As of 23:30 p.m. local time (2130 GMT), sounds of artillery shells could be heard in most neighborhoods of Tripoli," the source said, adding that the death toll could not be determined yet as the clashes were continuing.

The UN Support Mission in Libya (UNSMIL) called for an immediate halt to the violence.

"UNSMIL calls on the parties fighting now in the area of Salah Eddin in Tripoli to cease all hostilities immediately. UN holds the leaders of the fighting parties accountable for any harm befalling civilians, by their forces or groups affiliated with them," the mission said.

Clashes erupted in southern Tripoli since Tuesday morning, causing a power blackout in the south and west of the country, according to a security source.

Tripoli recently witnessed violent clashes between government forces and the so-called "Seventh Brigade" militia from the city of Tarhuna, some 80 km southeast of Tripoli.

UNSMIL recently brokered a ceasefire agreement between warring parties in Tripoli, ending heavy clashes that killed 78 people and injured 210 others. However, the Seventh Brigade threatened to break the truce in Tripoli and resume fighting to "eliminate crime and gangs in Tripoli."

Libya has been suffering insecurity and violence since the fall of former leader Muammar Gaddafi in 2011.