LONDON (AP) -- The top diplomats for Russia and the U.S. voiced pessimism Friday about negotiating an immediate end to the crisis in Ukraine, whose strategic Crimea region is voting this weekend about whether to secede.
Headed into a meeting in London, U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov each said they were glad to talk before the Sunday referendum in Crimea. The vote on the strategic Black Sea peninsula of 2 million people is widely expected to back secession and, potentially, annexation with Russia.
The U.S. and EU say the Crimean vote violates Ukraine's constitution and international law while Russia has said it will respect the results of the referendum.
The new government in Kiev believes the vote is illegal, but Moscow says it does not recognize the new government's leader as legitimate. If Crimea secedes, the U.S. and European Union plan to slap sanctions as early as Monday on Russian officials and businesses accused of escalating the crisis and undermining Ukraine's new government.
"This is a difficult situation we are in," Lavrov told reporters before meeting with Kerry at the U.S. ambassador's residence. "Many events have happened and a lot of time has been lost, so now we have to see what can be done."
Kerry said he hoped to unearth "possibilities that we may be able to find about how to move forward, together, to resolve some of the differences between us."
"Obviously we have a lot to talk about," Kerry 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 World War II era, when some residents cooperated 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 favors ties with the 28-nation European Union, while many in eastern Ukraine have closer economic and traditional ties to Russia. Vladimir Putin, Russia's leader, has worked for months to press Ukraine back into Russia's political orbit.
Russia engaged in more sable rattling Friday by warning that it reserves the right to intervene in eastern Ukraine in defense of ethnic Russians who it claims are under threat.
The Russian Foreign Ministry said clashes overnight Thursday in the eastern city of Donetsk showed that Ukrainian authorities had lost control over 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.
The U.N. assistant secretary-general for human rights, Ivan Simonovic, told reporters in Kiev on Friday 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 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 Kiev to de-escalate tensions. But British Prime Minister David Cameron on Friday 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 in London.
As Kerry and Lavrov met, U.K. Foreign Secretary William Hague said while it was "not too late" for the Crimea referendum to be canceled, 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.
Officials and experts say the vote of Crimea's majority ethnic Russian population will certainly result in a move to break away from Ukraine. Fearful residents on the peninsula have flocked to banks this week, trying to pull out whatever money they can.
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 in loan guarantees to Ukraine and International Monetary Fund revisions to help Kiev.