US Secretary of State John Kerry said on Saturday that the United States and Russia had agreed to exchange information about the situation on the Russia-Ukraine border.
Ukraine's military accused Russia on Friday of sending a column of 32 tanks and truckloads of troops into the country's east to support pro-Russian separatists fighting government forces.
"Suffice it to say that we do have some disagreements about some of the facts on the ground with respect to Ukraine. We have agreed to exchange some information between us regarding that. We have also agreed this is a dialogue between us that will continue," Kerry told reporters in Beijing.
But he seemed to suggest new Western sanctions against Russia were not imminent. "The choices Russia makes will decide what happens with respect to sanctions in the long run here," Kerry said, adding he hoped a ceasefire agreement in Ukraine would remain viable.
Russia has denied arming pro-Russian rebels in eastern Ukraine who have broken away from the Kiev government.
Before meeting Kerry in the lead-up to an Asia-Pacific Economic Cooperation (APEC) summit, Russian Foreign Minister Sergei Lavrov deflected a question about whether Moscow was sending tanks and troops to help the separatists.
Lavrov noted that the US government on Friday said that it was aware of the reports, but could not independently confirm them. "Even (spokeswoman) Jen Psaki said that the State Department doesn't have the information about this," he said. "Well, if Psaki doesn't have it, I don't."
"The ceasefire has been signed between the rebels and the government" in Kiev, Lavrov said. "It's for them to finalise the disengagement line which they are doing right now."
No talks are scheduled at the APEC summit between Russian President Vladimir Putin and US President Barack Obama though Washington and the Kremlin have not ruled out an informal conversation on the summit sidelines.