The Ukrainian crisis is becoming dire by the day, with the United States, European Union and Group of Seven (G7) countries set to impose tough new sanctions on Russia, even as Russian aircraft breached Ukraine's airspace several times over the past 24 hours, and pro-Moscow separatists seized a bus carrying international observers. Kiev has accused Russia of seeking to trigger a "third world war".
Armed pro-Russian separatists in Ukraine's eastern rebel-held town of Salvyansk detained a bus carrying 13 international mediators, earning immediate international condemnation.
The 13 observers are from the the Organization for Security and Cooperation in Europe (OSCE), and include three members of the German armed forces, a German translator and a Danish national, German Defence Minister Ursula von der Leyen has said.
According to the self-declared mayor of Slavyansk, the mediators were detained as they were believed to have a pro-Western Ukrainian spy amongst them from Kiev. The bus carrying the OSCE observers was detained at the entrance to the town, and the mediators were taken to a building held by the rebel forces.
The US has called for the immediate release of the international observers. According to State Department spokesperson Jen Psaki, there is a strong connection between Russia and the separatists.
According to the Pentagon, Russian aircraft have violated Ukraine's airspace several times over Thursday and Friday, escalating tensions between Kiev and Moscow.
Pentagon spokesperson Colonel Steven Warren did not provide details about what kind of planes were involved or where the airspace violations occurred, but urged Russia to take "immediate steps to de-escalate the situation".
Ukraine has stepped up its military operations against pro-Russian rebels in the country's east. Kiev's deputy foreign minister, Danylo Lubkivsky, said at the United Nations on Friday that his government would exercise restraint its moves against separatists. But if Russia crossed the border, "we will fight to defend our country," he said.
Ukrainian Prime Minister Arseniy Yatsenyuk accused Russia of wanting to trigger another World War, saying, "The world hasn't forgotten the Second World War and Russia wants to start a third world war."
"Russia's support for the terrorists in Ukraine constitutes an international crime and we call on the international community to unite against the Russian aggression."
Referring to Moscow's annexation of Crimea and its alleged efforts to destabilise eastern Ukraine by sponsoring the separatists, a Western diplomat voiced concern of a possible Russian move into eastern Ukraine in the coming days, maybe even over the weekend.
In the wake of Moscow's refusal to take steps to de-escalate the crisis in Ukraine, US, EU and G7 leaders have agreed to impose fresh sanctions on Russia. These sanctions could be imposed as early as Monday. Read: The full text of the G7 statement.
The EU is expected to name 15 previously unidentified individuals to be sanctioned, primarily those whom it believes are responsible for the unrest in Ukraine. Similarly, the US is expected to target individuals and entities it has identified as "cronies" of Russian President Vladimir Putin.
With inputs from agencies.