Hundreds of pro-Russian separatists in eastern Ukraine seized another regional government headquarters on Tuesday.

This one, in Luhansk, where they were unopposed by police.

The central government has all but lost control of its police forces in parts of eastern Ukraine.

That's were an armed rebel movement seeks more autonomy or outright annexation into neighboring Russia.

Evicting the separatists has been a struggle for authorities.

On Tuesday, Ukrainian Prime Minister Arseny Yatseniuk urged parliament to adopt a new constitution to prevent further unrest.

(SOUNDBITE) (Ukrainian) ARSENY YATSENIUK, PRIME MINISTER OF UKRAINE, SAYING:

"The Ukrainian Constitution must become a document of national unity; the unity that is highly needed in this country; the unity which is the only guarantee for preserving the Ukrainian state…and will preserve it as an integral, independent, European state where every Ukrainian has his legal place."

Tuesday mo