Top US diplomat, John Kerry, has met with his Russian counterpart Sergei Lavrov in London on Friday in a last-minute bid to stave off escalating tensions in the East-West crisis over Ukraine.

Kerry was expected to press Lavrov to de-escalate the situation in Ukraine's Black Sea peninsula of Crimea, where Russian troops promptly seized control after the recent ouster of Ukraine's pro-Kremlin president Viktor Yanukovych.

Following the ouster, pro-Moscow authorities in Crimea have organized a referendum for Sunday in the mainly Russian-speaking region, which is also home to Russia's Black Sea fleet. The referendum has been widely rejected as illegitimate by Western powers and is expected to bring the simmering crisis to a head.

Russian President Vladimir Putin has said he was answering calls for help from ethnic Russians who believed they were threatened by EU supporters in Ukraine. Moscow does not recognize the legitimacy of Ukraine's transitional government.

Kerry has warned Russia that the US and the EU will impose sanctions against Russia as soon as Monday if the referendum goes ahead.

Diplomacy over aggression

On Thursday, both Ukraine and Russia insisted during a UN Security Council session that they did not want war. It was the sixth meeting of the Security Council on Ukraine in less than two weeks. With Russia a permanent member, with veto powers, the council has been unable to take any action over the ongoing crisis.

Addressing Thursday's emergency session, Ukraine's interim Prime Minister Arseniy Yatsenyuk urged Russia to negotiate an end to the stand-off.

"We want to have talks. We don't want to have any kind of military aggression," he insisted.

Yatsenyuk said he was convinced that "Russians do not want war," and at one point switched from English to Russian, directly asking Russia's UN ambassador Vitaly Churkin if this was the case.

In his speech, Churkin replied that "Russia does not want war and nor do the Russians, and I'm convinced that Ukrainians don't want this either."

Despite the calming rhetoric, at least one person was stabbed and killed in Ukraine's eastern city of Donetsk, when pro-Kyiv demonstrators were allegedly attacked by a pro-Russia group. It was the first confirmed death since Crimea was seized.

hc/ipj (Reuters, AFP, AP)