U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov are holding talks in London on the Ukraine crisis.
Kerry, who has warned that the West would take "very serious steps" if Russia goes ahead with the annexation of Crimea, said before the meeting the two would discuss how best to smooth over their differences.
"Obviously, we have a lot to talk about. I look forward to an opportunity to dig into the issues and possibilities that we may be able to find about how to move forward together to resolve some of the differences between us," Kerry said.
Kerry was expected to tell Lavrov that Russia risks concerted international sanctions because of the March 16 referendum on Crimea joining Russia.
Lavrov told reporters in London that precious time has been wasted in resolving the crisis: "I am also satisfied to have this meeting today. This is a difficult situation we are in. Many events have happened and a lot of time has been lost, so now we have to see what can be done."
British Foreign Minister William Hague, who held talks with Kerry earlier in London, said the talks represent a "formidably difficult task."
Donetsk Violence
Meanwhile, Russia's Foreign Ministry said in a statement that overnight violence in eastern Ukraine demonstrates that authorities in Kyiv are losing control and that Russia reserves the right to protect its citizens.
The statement came as tensions rose in Ukraine's east, where a 22-year-old man was stabbed to death on March 13 in Donetsk as pro-European demonstrators were attacked by pro-Russian supporters.
The Foreign Ministry noted that one person was killed in the violence in Donetsk and said "Russia is aware of its responsibility for the lives of fellow citizens and compatriots in Ukraine and reserves the right to take people under its protection."
However, organizers of the pro-EU rally said the dead man was from their group.
The United Nations on March 14 said it was deploying human rights monitors throughout Ukraine, including in Crimea, to establish the facts surrounding claims of rights abuses.
In a statement, Assistant Secretary-General for Human Rights Ivan Simonovic said placing monitors in Ukraine is necessary to clear up the "preponderance of competing narratives about what exactly has transpired in the country since November."
Earlier this week, Simonovic was unable to visit Crimea as the local authorities stated that they would not receive the mission nor ensure its security.
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Rival Protesters Clash In Donetsk
(WATCH: Rival Protesters Clash In Donetsk)
Russia, meanwhile, has called on the Organization for Security and Cooperation in Europe (OSCE) to send observers to monitor Sunday's controversial referendum in Crimea, which is occupied by Russian forces.
The Foreign Ministry said in a statement that the OSCE should renounce what it called the practice of "double standards" and monitor the vote. But OSCE Chairman Didier Burkhalter has said the referendum in Crimea "must be considered illegal" in its current form.
On March 13, Russian Ambassador to the UN Vitaly Churkin said Russia did not want war in Ukraine, but advocated Crimea's right to self-determination.
He spoke after Russia began new military exercises -- involving 8,500 troops -- near its border with Ukraine.
In a sign of support for NATO's eastern members, U.S. F-16 fighter jets landed Thursday in Poland.
