Ukraine's Prime Minister Yatseniuk and OSCE observers attend a welcoming ceremony and a news conference at Boryspil International airport outside Kiev
Ukraine's Prime Minister Arseny Yatseniuk (4th L) and OSCE observers attend a welcoming ceremony and a news conference at Boryspil International airport outside Kiev May 3, 2014. A group of military observers who were seized last week by pro-Russian separatists in the eastern Ukrainian city of Slaviansk has been released, the Organization for Security and Cooperation in Europe (OSCE) confirmed on Saturday. REUTERS/Maks Levin (UKRAINE - Tags: POLITICS CIVIL UNREST)
Ukraine's Prime Minister Yatseniuk and OSCE observers walk to attend a welcoming ceremony and a news conference at Boryspil International airport outside Kiev
Ukraine's Prime Minister Arseny Yatseniuk (L, front) and OSCE observers walk to attend a welcoming ceremony and a news conference at Boryspil International airport outside Kiev May 3, 2014. A group of military observers who were seized last week by pro-Russian separatists in the eastern Ukrainian city of Slaviansk has been released, the Organization for Security and Cooperation in Europe (OSCE) confirmed on Saturday. REUTERS/Maks Levin (UKRAINE - Tags: POLITICS CIVIL UNREST)
Ukraine's Prime Minister Yatseniuk and OSCE observers walk to attend a welcoming ceremony and a news conference at Boryspil International airport outside Kiev
Ukraine's Prime Minister Arseny Yatseniuk (L, front) and OSCE observers walk to attend a welcoming ceremony and a news conference at Boryspil International airport outside Kiev May 3, 2014. A group of military observers who were seized last week by pro-Russian separatists in the eastern Ukrainian city of Slaviansk has been released, the Organization for Security and Cooperation in Europe (OSCE) confirmed on Saturday. REUTERS/Maks Levin (UKRAINE - Tags: POLITICS CIVIL UNREST)
Ukraine's Prime Minister Yatseniuk and OSCE observers attend a welcoming ceremony at Boryspil International airport outside Kiev
Ukraine's Prime Minister Arseny Yatseniuk (front) and OSCE observers attend a welcoming ceremony at Boryspil International airport outside Kiev May 3, 2014. A group of military observers who were seized last week by pro-Russian separatists in the eastern Ukrainian city of Slaviansk has been released, the Organization for Security and Cooperation in Europe (OSCE) confirmed on Saturday. REUTERS/Maks Levin (UKRAINE - Tags: POLITICS CIVIL UNREST)
OSCE observers walk down the stairs upon their arrival at Boryspil International airport outside Kiev
OSCE observers walk down the stairs upon their arrival at Boryspil International airport outside Kiev May 3, 2014. A group of military observers who were seized last week by pro-Russian separatists in the eastern Ukrainian city of Slaviansk has been released, the Organization for Security and Cooperation in Europe (OSCE) confirmed on Saturday. REUTERS/Maks Levin (UKRAINE - Tags: POLITICS CIVIL UNREST TRANSPORT)
Armed pro-Russian activists take positions in Luhansk
Armed pro-Russian activists take positions in Luhansk, eastern Ukraine, May 3, 2014. The shooting with automatic weapons started between pro-Russian activists and presumably Ukrainian police near the building of the regional military commissariat. REUTERS/Vasily Fedosenko (UKRAINE - Tags: POLITICS CIVIL UNREST)
An armed pro-Russian activist runs in Luhansk, eastern Ukraine
An armed pro-Russian activist runs in Luhansk, eastern Ukraine, May 3, 2014. The shooting with automatic weapons started between pro-Russian activists and presumably Ukrainian police near the building of the regional military commissariat. REUTERS/Vasily Fedosenko (UKRAINE - Tags: POLITICS CIVIL UNREST)
Armed pro-Russian activists take positions in Luhansk
Armed pro-Russian activists take positions in Luhansk, eastern Ukraine, May 3, 2014. The shooting with automatic weapons started between pro-Russian activists and presumably Ukrainian police near the building of the regional military commissariat. REUTERS/Vasily Fedosenko (UKRAINE - Tags: POLITICS CIVIL UNREST)
Armed pro-Russian activist runs in Luhansk
An armed pro-Russian activist runs in Luhansk, eastern Ukraine, May 3, 2014. The shooting with automatic weapons started between pro-Russian activists and presumably Ukrainian police near the building of the regional military commissariat. REUTERS/Vasily Fedosenko (UKRAINE - Tags: POLITICS CIVIL UNREST)
Armed pro-Russian activists take positions in Luhansk, eastern Ukraine
Armed pro-Russian activists take positions in Luhansk, eastern Ukraine, May 3, 2014. The shooting with automatic weapons started between pro-Russian activists and presumably Ukrainian police near the building of the regional military commissariat. REUTERS/Vasily Fedosenko (UKRAINE - Tags: POLITICS CIVIL UNREST)