Washington and the international community won't recognize the outcome of Sunday's referendum in Crimea on seceding from Ukraine, U.S. Secretary of State John Kerry said Friday after six hours of talks with Russia's foreign minister.

"Neither we nor the international community will recognize the results of this referendum and we also remain deeply concerned about the large deployments of Russian forces in Crimea and along the eastern border," Kerry said.

"Right now, given this particular climate, we really need to hear more declarative policy in order to make clear where Russia is proceeding with respect to these troops and these exercises."

His comments came after Russian Foreign Minister Sergey Lavrov acknowledged there was no "common vision" between the two nations over the crisis in Ukraine.

Sunday's vote on Crimea — Ukraine's strategic Black Sea peninsula of two million people — is widely expected to back secession and, potentially, annexation with Russia. The new government in Kyiv believes the vote is illegal, but Moscow says it does not recognize the new government as legitimate.

Kerry said he also raised concerns over the troop movements during the talks with Lavrov in London.

"The Foreign Minister made it clear that President Putin is not prepared to make any decision regarding Ukraine until after the referendum on Sunday," Kerry said.

"We believe the referendum is contrary to the constitution of Ukraine, contrary to international law, is in violation of that law, and is illegitimate."

Also on Friday Prime Minister Stephen Harper announced via Twitter that he will briefly visit Ukraine next week during a European trip. He will be the first G7 leader to do so since the new government took office.

And U.S. Vice President Joe Biden will travel to Poland, which borders Ukraine, and Lithuania next week to meet with leaders of the two countries to reassure them about defence commitments under NATO, the White House said on Friday.

Lavrov on Friday reaffirmed that Russia will "respect the results of the referendum" in Crimea and said sanctions would harm relations.

"Our partners also realize that sanctions are counterproductive," he said.

European and U.S. leaders have repeatedly urged Moscow to pull back its troops in Crimea and stop encouraging local militias there who are hyping the vote as a choice between re-establishing generations of ties with Russia or returning to echoes of fascism from Ukraine's Second World War era, when some residents co-operated with Nazi occupiers.

The showdown between Russia and the West has been cast as a struggle for the future of Ukraine, a country with a size and population similar to France. Much of western Ukraine favours ties with the 28-nation European Union, while many in eastern Ukraine have closer economic and traditional ties to Russia. Vladimir Putin, Russia's president, has worked for months to press Ukraine back into Russia's political and economic orbit.

While the Russian Foreign Ministry engaged in more sabre-rattling Friday by warning that it reserves the right to intervene in eastern Ukraine in defence of ethnic Russians who it claims are under threat, Lavrov denied any plans to send troops into eastern Ukraine.

"Russia doesn't and can't have any plans to invade southeastern regions of Ukraine," he said.

Clashes in eastern city

The Russian Foreign Ministry said clashes overnight Thursday in the eastern city of Donetsk showed that Ukrainian authorities had lost control of the country and could not provide basic security.

The clashes broke out, however, when a hostile pro-Russian crowd confronted pro-government supporters. At least one person died and 29 were injured.

Ukraine responded by calling the Russian statement "impressive in its cynicism."

"[The Donetsk clashes had] a direct connection to deliberate, destructive actions of certain citizens of Russia and some Russian social organizations, representatives of which are present in our country to destabilize the situation and escalate tensions," Ukrainian Foreign Ministry spokesman Evgeny Perebiynis said, according to the Interfax news agency.

The UN assistant secretary-general for human rights, Ivan Simonovic, told reporters Friday in Kyiv that there was "no sign of human rights violations of such a proportion, of such widespread intensity that would require any military measures."

Russia has also sent thousands of troops to its long border with Ukraine, a move that U.S. officials have called an intimidation tactic cloaked as military exercises. The Russian drills announced Thursday included large artillery exercises involving 8,500 soldiers in the Rostov border region alone.

Western officials have asked Russia to start diplomatic talks with Kyiv to lessen tensions but Russia says that government illegally drove Ukraine's pro-Russian president from power.

British Prime Minister David Cameron underlined the threat of sanctions.

"We want to see Ukrainians and the Russians talking to each other. And if they don't, then there are going to have to be consequences," Cameron told Kerry in a separate meeting Friday in London.

'Difficult task'

U.K. Foreign Secretary William Hague said while it was "not too late" for the Crimea referendum to be cancelled, it was important to be "realistic" about the prospects.

"The fact that so far Russia has not taken any actual action to de-escalate the tensions makes this a formidably difficult task today," Hague said.

Kerry arrived in London with plans to make clear to Lavrov about the stakes that Russia faces. The U.S. wants Russia to accept something short of a full annexation of Crimea — but Kerry has not said what that might entail.

He told senators in Washington that should the Crimea vote take place and no resolution is reached, "there will be a very serious series of steps on Monday in Europe and here."

Obama has imposed limited sanctions against unidentified Russian officials thought by the U.S. to be directly involved in destabilizing Ukraine.

But Congress on Thursday put off a vote until after March 24 that would have expanded those sanctions, as well as approve $1 billion US in loan guarantees to Ukraine and International Monetary Fund revisions to help Kyiv.

With files from Reuters