The head of the U.N. mission to Libya says the new unity government will install itself in Tripoli within days.

Martin Kohler told reporters on Tuesday that he doesn't have the exact date but, "I know it's a matter of days not weeks."

In Libya, where chaos reigns and the Islamic State group has a new foothold, two rival governments compete. Kohler said "it is urgent to stop the expansion" of the IS group into neighboring countries, like Tunisia.

The head of the new government, Faez All-Sarraj, said that "we must react quickly" to stop the "cancer." He called on Libyans to set aside differences and build a new, safe Libya.

The two spoke after a ministerial meeting of Tunisia, Algeria, Egypt, Chad, Sudan and Niger, all threatened by extremists.