GENEVA -- U.S. Secretary of State John Kerry is meeting his Russian counterpart for likely highly contentious talks amid continuing tensions over Ukraine and American calls for a full probe into the murder of a prominent opposition figure in Moscow.

Neither Kerry nor Russia's Foreign Minister Sergey Lavrov smiled or spoke substantively as they shook hands before photographers at a Geneva hotel on Monday, less than a week after Kerry told Congress that Russian officials have lied to his face about Moscow's role in Ukraine.

The comment drew a rebuke from the Russian foreign ministry. U.S. officials have pointed out that Kerry did not specifically accuse Lavrov of lying to him. They say he was referring to public statements and media reports although Lavrov is the only Russian official Kerry has been known to have met face-to-face in recent months. They last met on the sidelines of an international security conference in Munich shortly before a new Ukraine ceasefire agreement was agreed upon.

Both Ukraine and the Russian-backed rebels have accused each other of violating the truce and the meeting comes as the U.S. and its European allies contemplate additional sanctions on Russia for its actions in Ukraine. In his congressional testimony last week, Kerry said that fresh U.S. sanctions had already been prepared and suggested they could be implemented soon. However, U.S. officials have said since that they will wait to see if the ceasefire and follow-on commitments to end the violence in Ukraine's east are complied with before putting the sanctions in place.

Monday's meeting also follows Friday's murder near the Kremlin of Russian opposition leader Boris Nemtsov. Kerry and other U.S. and western officials have called on Russia to conduct a prompt, thorough, transparent and credible investigation into the slaying. Russian President Vladimir Putin has said he will take personal charge of the probe. U.S. officials travelling with Kerry would not say what they thought of Putin's move and said they would withhold comment until the investigation is complete.