Emergency meeting on Ukraine

All updates in Universal Coordinated Time (UTC)

20:15 - US President Barack Obama has said that he spoke with German Chancellor Angela Merkel and they agree that Russia is responsible for the violence in eastern Ukraine. Russia's "ongoing incursion" would only worsen the situation, Obama said. He also announced that Ukrainian President Petro Poroshenko would visit the White House next month.

19:30 - At the UN Security Council meeting, the US and several other members voice condemnation of alleged incursion into Ukraine, calling for an immediate withdrawal of Russian forces. "Serious negotiations are needed, but Russia has to stop lying and has to stop fueling this conflict," said Samantha Power, US ambassador to the UN. During the emergency session in New York, Power spoke of the urgency of the situation on her Twitter account:

18:28 - Moscow reiterates position that it hasn't crossed the Ukrainian border with military vehicles, according to Kremlin EU ambassador. Vladimir Chizhov told the British Broadcasting Corporation that only 10 Russian soldiers were currently on Ukrainian grounds, troops he called "volunteers."

18:19 - As UN Security Council meets in New York, United States government warns of possible "further sanctions" against Russia for its "role in the current fighting" in Ukraine. "We have additional tools and sanctions that we can certainly choose to put in place," State Department spokeswoman Jen Psaki said.

18:05 - UNSC convenes emergency meeting to discuss ways to help de-escalate situation in eastern Ukraine.

16:25 Germany's Chancellor warns that Russia could now face tougher sanctions as a result of the escalation of the conflict in eastern Ukraine. Angela Merkel said EU ministers are scheduled to meet on Saturday. "We are getting reports of an increased presence of Russian soldiers and of new unrest and fresh advances of the separatists in areas that until now were very quiet," she told a news conference on Thursday after talks with Balkan leaders.

16:23 - Spokesman for UN Secretary General Ban Ki-Moon calls reports of firing in Ukraine a "dangerous escalation." "The international community cannot allow the situation to escalate further nor can a continuation be allowed of the violence and destruction that the conflict has wrought in eastern Ukraine," UN spokesman Stephane Dujarric told reporters.

16:20 - Russia rejects claims that its military is stationed in Ukraine. Defense spokesman quoted by Interfax as saying allegations of Russian presence in eastern Ukraine bear "no relation to reality."

15:35 - North Atlantic Treaty Organization says ambassadors of its 28 members and Ukraine will hold an emergency meeting on Friday to discuss the situation. Ukraine is not a NATO member but meets regularly with the organzation in a body called the NATO-Ukraine Commission.

14:57 - NATO Spokeswoman Oana Lungescu, on official NATO Twitter account, publishes satellite imagery displaying ostensible Russian presence inside Ukraine.

14:41 - Ukrainian President Petro Poroshenko tells Interfax that situation is "difficult, yet controllable," following losses to Russian forces in eastern Ukraine. Poroshenko, who met with top security and defense chiefs after the key town of Novoazovsk fell to Russian-backed separatists, said Russian troops had come "to the rescue" of the rebels after Kyiv's earlier military successes.

14:32 - Russian state broadcaster, RT, via Berlin-based video news agency Ruptly, publishes footage of separatists in Novoazovsk raising flag atop municipal building.

14:22 - The UN Security Council is to hold an emergency meeting Thursday on the Ukraine crisis. "Russia will be asked to explain why it has its troops inside Ukraine," British Ambassador Mark Lyall Grant, whose country holds the presidency of the Security Council, told journalists.

13:41 - Associated Press journalists report Russian military vehicles in Novoazovsk.

13:32 - Polish foreign minister says Russia's actions in Ukraine constitute aggression. "Most serious security crisis in decades," Radoslaw Sikorski told the Reuters news agency.

13:04 - The foreign ministers of Romania, Moldova and and Georgia weigh in on the crisis, at a meeting in Bucharest their Ukrainian counterpart was also meant to attend. Romanian Foreign Minister Titus Corlatean said the situation was "extremely, extremely grave." Georgian Foreign Minister Maia Panjikidze called the developments in eastern Ukraine "alarming news."

12:04 - A senior NATO official has said that "well over 1,000 Russian troops" are stationed and operating within Ukraine. "They support separatists, fighting with them and fighting amongst them," the official said on condition of anonymity.

11:46 - Russian Ambassador to the OSCE Andrey Kelin has separately told reporters during the body's extraordinary meeting that, "No Russian forces are crossing in any point the border of Ukraine."

11:17 - Ukraine's ambassador to the Organization for Security and Cooperation in Europe (OSCE) has accused Russia of a "direct invasion." "We registered a direct invasion by the Russian military into the eastern regions of Ukraine," Ihor Prokopchuk told journalists in Vienna following a special meeting of the European security body. Prokopchuk cited the capture "by regular Russian forces" of the key southeastern town of Novoazovsk and several other surrounding towns.

11:02 - Ukraine's President Petro Poroshenko said Russian forces had been brought into Ukraine: "I made the decision to cancel a working visit to the Republic of Turkey in connection with the rapidly deteriorating situation in Donetsk region, in particular in Amvrosiyivka and Starobesheve, as Russian troops have actually been brought into Ukraine," he said in a statement on the presidential website.

glb/jr (Reuters, AFP, AP, dpa)