The State Department on Monday said it was “still awaiting” a Russian response to the Obama administration's demands that it withdraw troops from Ukraine's Crimean peninsula and stop promoting a referendum on seceding in the territory.

Reports said Russian forces had advanced further in the Crimean peninsula, ignoring U.S. calls to pull back and respect Ukraine's sovereignty and territorial lines.

Secretary of State John Kerry talked to Russian Foreign Minister Sergey Lavrov on Saturday about the intensifying crisis, telling his counterpart that he wanted to see “a cessation of Russian military advances in Ukraine, including Ukraine's Crimean Peninsula, a halt in the drive for annexation of Crimea, and the end of provocative steps to provide space for diplomacy,” State Department spokeswoman Jen Psaki said in a statement Monday.

“The United States needs to see concrete evidence that Russia is prepared to engage on the diplomatic proposals we have made to facilitate direct dialogue between Ukraine and Russia and to use international mechanisms like a contact group to de-escalate the conflict,” Psaki said.

“We are still awaiting a Russian response to the concrete questions that Secretary Kerry sent Foreign Minister Lavrov on Saturday in this regard,” she added.

Psaki’s statement came amid reports that Lavrov had requested that Kerry visit Moscow for further discussions.

Psaki said Kerry made clear to Lavrov that he would welcome further discussions focused on how to de-escalate the crisis in Ukraine “if and when we see concrete evidence that Russia is prepared to engage on these proposals.”

Kerry is scheduled to testify before the House Foreign Affairs Committee on Thursday on Obama's budget request for the State Department, where he will likely face tough questions on the administration’s handling of the Crimean crisis.

Ukrainian Prime Minister Arseniy Yatsenyuk said Sunday he planned to travel to Washington this week for meetings with U.S. officials.

Pro-Russian lawmakers in the Crimea region voted Thursday to join the Russian Federation and announced a referendum vote March 16.

The Obama administration views the vote to annex Crimea as an illegal attempt to redraw Ukraine's borders in an attempt to circumvent the interim government.