UNSMIL said in a statement Monday it condemned attacks on members of the General National Congress and the vandalizing of the building housing the political body.
"The mission stresses the importance of respecting the legitimate institutions, rejecting violence in politics and guaranteeing the right to free expression through peaceful means, all of which ensure the proper continuation of the political process aiming to achieve a democratic transfer of power and preserve the security and stability of Libya," it said.
At least two members of the GNC were wounded when demonstrators stormed their Tripoli headquarters Sunday, CNN International reported. It said public frustration with Libyan lawmakers mounted in December when GNC members voted to extend their term through the end of the year.
It's the second such attack in the GNC in as many weeks. Last week, UNSMIL said it had "deep" concerns about continued violence in Libya, including assassinations and attacks on judicial and political leaders, polling centers and buildings housing government buildings.
Libya has struggled to maintain a level of national security since then because of violent internal rivalries.