The United States and Russia failed on Friday to resolve a Cold-War-style crisis sparked by Moscow's military intervention in Crimea and the Ukrainian peninsula's weekend referendum on joining Kremlin rule.
US Secretary of State John Kerry met his Russian counterpart Sergei Lavrov in London with few hopes that Sunday's Moscow-backed referendum in the strategic Black Sea peninsula that has been seized by Kremlin troops could be averted or delayed.
But US officials indicated that they still expected Moscow to avoid taking the extra step of actually annexing the region of two million mostly Russian speakers in a move that would escalate the biggest East-West showdown since the 1989 fall of the Berlin Wall.
Lavrov however told reporters after more than three hours of talks with Kerry at the lavish US ambassador's residence in central London that Russia and the West still had "no common vision" on Ukraine.
"We have no common vision of the situation," said Lavrov. "Differences remain."
Lavrov added that Russia would "respect the will of the Crimean people" in the referendum result.
Kerry was expected to meet reporters later Friday.
US President Barack Obama had only moments earlier said in Washington that he still held out hope of a diplomatic solution while warning Moscow of "consequences" if none was found.
The self-declared pro-Kremlin head of Crimea who initially called the controversial referendum gave Western negotiators some hope by indicating that he did not expect Russia to annex his region right away.
"It would take a maximum of one year," Sergiy Aksyonov told reporters in the Crimean capital of Simferopol.
Ukraine itself remained a tinderbox as more than 8,000 Russian troops staged drills near its eastern border while NATO and US reconnaissance aircraft and fighters patrolled the skies of the ex-Soviet state's EU neighbours to the west.
Kerry has warned Russia that Washington and Europe could announce a "very serious" response as early as Monday if Moscow does not pull back the troops who seized control of Crimea days after the pro-Kremlin regime fell in Kiev last month.
"The first thing that Secretary Kerry will say is 'will you use your influence to buy time and space for negotiations to take place?'," one US official said ahead of the Kerry-Lavrov talks.
Yet Russia still refuses to recognise the legitimacy of the Western-leaning team that has taken power in Kiev -- a move that threatens to shatter President Vladimir Putin's dream of rebuilding a Soviet-type empire.
The diplomatic drama played out before a global audience at the United Nations on Thursday when Ukraine's new prime minister Arseniy Yatsenyuk turned to Moscow's UN representative Vitaly Churkin and asked him directly: "Do the Russians want war?"
Churkin replied that Russia did not. But he also repeated Putin's argument that Yatsenyuk and his allies had conducted the "forceful overthrow" of Moscow-backed president Viktor Yanukovych that created a "government of victors" and not of Ukraine's democratic majority.
Deadly violence meanwhile returned to Ukraine for the first time since nearly 90 people were killed in a week of carnage before the fall of the pro-Kremlin regime as a pro-Kiev protester was stabbed to death in the mostly Russian-speaking city of Donetsk.
The local health service said a 22-year-old man died and 16 people were wounded in unrest that erupted when pro-Kiev demonstrators were attacked by pro-Moscow protesters.
Ukraine's acting President Oleksandr Turchynov blamed the death on separatists "sent in" from Russia.
"These people and the Kremlin do not care about the lives of those they claim to be protecting," Turchynov said in a statement.
But the Russian foreign ministry blamed the violence on the new leaders' inability to "have the situation under control" and once again reaffirmed its right to intervene in its western neighbour's affairs.
"Russia recognises its responsibility for the life of its compatriots and fellow citizens in Ukraine and reserves the right to protect people," the Russian foreign ministry said.
Sunday's vote gives residents of Crimea -- a Russian-speaking region that has housed tsarist and Kremlin navies since the 18th century -- only two choices: joining Russia or "the significant strengthening of their autonomy within Ukraine".
The peninsula's self-declared leaders have already predicted an easy victory and the region is largely expected to vote in favour of joining Russia despite discontent from the Muslim Tatar minority that makes up 12 percent of Crimea's total population of two million.
Tatar community leader Mustafa Dzhemilev told AFP on Thursday that NATO should intervene in Crimea to avert a "massacre" of his people by the Russians.
But Washington and its European allies are far more likely to stiffen sanctions against top Russians should the Kremlin fail to scale down its military involvement in Crimea and open direct dialogue with Kiev.
"If there is no sign of any capacity to be able to move forward and resolve this issue, there will be a very serious series of steps on Monday in Europe and here with respect to the options that are available to us," Kerry told lawmakers in Washington.
The European Union will debate travel bans and asset freezes on Monday against Russian officials held responsible for threatening Ukraine's territorial integrity.
The White House has been moving toward punitive measures faster than its European allies -- whose financial and energy sectors are tightly intertwined with Russia's -- and has already approved visa restrictions and financial penalties on Moscow officials.
US officials have stressed that Putin himself is not on the sanctions list.
But US President Barack Obama told Yatsenyuk after talks in the Oval Office that Washington was willing to move much further still if Putin failed to soften his stance immediately.