"The United Nations Support Mission in Libya (UNSMIL) deeply regrets the continued blatant violations of the arms embargo in Libya, even after the commitments made in this regard by concerned countries during the International Conference on Libya in Berlin," UNSMIL said in a statement.
On Jan. 19, participants of the Berlin conference agreed to respect an arms embargo imposed on Libya by the UN Security Council.
Numerous cargo and other flights have been observed landing at airports in eastern and western Libya over the past few days, providing advanced weapons, armored vehicles, advisers and fighters to relevant parties to the conflict, according to the statement.
"The mission condemns these ongoing violations, which risk plunging the country into a renewed and intensified round of fighting," it added.
The eastern-based army has been leading a military campaign since early April in an attempt to take over Tripoli from the UN-backed government.
The conflict killed and injured thousands of people, and displaced more than 150,000 civilians.
The two rival parties, which agreed to a ceasefire on January 12, accused each other of breaching the truce.