An estimated 1,000 Russian soldiers have reportedly crossed Ukraine's southern border to join Russian-backed separatists in their fight against Ukrainian forces.
"Such actions taken by the Russian Federation are a gross violation of fundamental principles of international law and agreements reached at international meetings. These actions openly violate Ukraine's sovereignty and territorial integrity, and undermine security across the entire region," Lithuania's foreign ministry wrote in its request that "the United Nations Security Council discuss this matter immediately."
Ukrainian Prime Minister Arseniy Yatsenyuk reached out Thursday to Western partners, asking them to request a special meeting of the U.N. Security Council, and also urged the OSCE and European Union to convene at the foreign minister level.
The U.N. Security Council emergency session is scheduled for 2:00 p.m. EDT.
Notable deaths of 2014 [PHOTOS]