Russian Defense Minister Sergei Shoigu has assured U.S. Defense Secretary Chuck Hagel that Russia will not invade Ukraine.
The two defense chiefs spoke by phone on April 28.
Russia's Defense Ministry said Shoigu told Hagel that Russian troops had returned to barracks after conducting exercises on Ukraine's border.
He said they did so after "Ukrainian authorities declared they would not use regular military units against the unarmed [Ukrainian] population."
Shoigu also called the increase in activity of U.S. and NATO forces near Russia's borders unprecedented.
About 150 U.S. troops arrived in Estonia on April 28 to take part in military exercises amid rising tensions with Russia over Ukraine.
The deployment brings to 600 the number of troops sent by Washington to Poland and the Baltic states during the crisis.
The United States this week imposed sanctions on Igor Sechin, a close confidant of Russian President Vladimir Putin, as well as six other senior officials and 17 Russian companies in response to what it calls Moscow’s “indisputable” role in recent violence in Ukraine.
Sechin, chairman of Russian state-owned oil major Rosneft, is widely seen as one of the country’s most powerful individuals after Putin.
"We've consistently felt that there are a range of officials with close ties to President Putin who have supported these illegal acts in Ukraine that we can target here," U.S. State Department spokeswoman Jen Psaki told reporters in Washington.
The new measures mark the third wave of sanctions in response to Russia’s annexation of Ukraine’s Crimea region.
Meanwhile, diplomats say the European Union has agreed to add 15 more names to its list of individuals hit by sanctions in response to Russia's actions in Ukraine.
The diplomats said ambassadors of the EU's 28 nations agreed to broaden the bloc's sanctions list at a meeting in Brussels on April 28.
The 15 individuals will be subjected to visa bans and asset freezes.
The names of those added to the list will not be made public until they are published in the EU's Official Journal.
In other developments, Moscow said on April 28 that it was "irresponsible" to send international observers to eastern Ukraine.
"People [in eastern Ukraine] are expecting an aggression or an offense every moment, so [the situation there] is extremely tense. That is why it was extremely irresponsible to direct [OSCE monitors] to this region in this tense situation," Russian envoy to the Organization for Security and Cooperation in Europe (OSCE) Andrei Kelin said in Vienna.
Pro-Russian separatists in the eastern city of Slovyansk captured eight international OSCE observers on April 15. One, a Swede, has been released on medical grounds.
The others are still being held, described by the separatists' leader as "prisoners of war."
In new violence, several people were reported wounded when pro-Russian separatists on April 28 attacked a rally in support of Ukrainian unity in Donetsk.
Media reports said dozens of men dressed in military fatigues and wielding baseball bats and iron bars attacked the rally of some 2,000 people.
Meanwhile, Ukraine's acting President Oleksandr Turchynov has ordered the Interior Ministry and State Security Service to jointly investigate the shooting of the mayor of the eastern city of Kharkiv.
Hennadiy Kernes was shot in the back by an unknown gunman around noon on April 28 while bicycling near Kharkiv.
With reporting by AP, AFP, and Reuters