The U.S. says it will make a decision "in days" whether to impose new sanctions on Russia if Moscow does not make an effort to implement an agreement signed in Geneva last week.
U.S. State Department spokeswoman Jen Psaki said in Washington on April 21 that the U.S. expects Russia to publicly call on pro-Russian separatists in eastern Ukraine to leave buildings they occupy and to abandon checkpoints they have set up.
She said those armed activists should accept an amnesty offered by the Ukrainian government and use political means to express their demands.
Psaki said the U.S. will decide "in a matter of days" whether or not Russia has made an effort to implement the accord on the de-escalation in Ukraine, known as the Geneva agreement.
U.S. Secretary of State John Kerry has called on Russia to take “concrete steps” to implement the agreement.
Russian Foreign Minister Sergei Lavrov has meanwhile called on Washington to use its influence to pressure the Western-backed Ukrainian authorities to implement their part of the agreement.
The United States and Russia each released statements following a telephone call between Kerry and Lavrov on April 21.
The State Department said Kerry had already urged Russia to publicly call on separatists to vacate buildings and checkpoints they have illegally occupied.
The Russian Foreign Ministry said Lavrov had urged Kerry to pressure Ukrainian authorities to crack down on ultranationalists and prevent "hotheads" from provoking a conflict.
Kerry and Lavrov joined their counterparts from Ukraine and the European Union in negotiating the April 17 Geneva agreement.
The accord calls for all Ukrainian illegal armed groups to disarm, and for all protesters to end their occupation of public facilities.
Amid high tensions over the seizure by pro-Russian militants of towns in east Ukraine, little progress in implementing the agreement has been reported so far.
Russia has blamed Ukrainian nationalists for stirring up problems in eastern Ukraine, including the April 20 shooting near the town of Slovyansk in which at least three people died.
Russia accuses members of Ukraine's Right Sector ultranationalist group of carrying out that attack.
Authorities in Kyiv and the Right Sector have denied any connection to the violence, and have instead accused Russia of carrying out a provocation.
Meanwhile, U.S. Vice President Joe Biden has arrived in Kyiv to start a visit in which he is expected to hold talks with the Ukrainian leadership.
A senior U.S. administration official said the vice president plans to announce during his two-day visit a package of technical assistance to Ukraine, focused on energy and economic aid.
The official said the assistance includes technical aid to help boost efficiency in natural gas fields and extraction of unconventional energy resources.
Concerns about Ukrainian energy supplies have soared since Russia sharply increased the prices that Ukraine must pay for Russian gas. Moscow's move came as tensions surged following Russia's annexation of Ukraine's Crimea in March.
Biden is to meet with acting President Oleksandr Turchynov, Prime Minister Arseniy Yatsenyuk, and members of Ukraine's parliament on April 22.
WATCH: Biden arrives in Ukraine
In other developments, Russia's Central Bank on April 21 ordered the activities of four Ukrainian banks in Crimea to be halted.
And Russian President Vladimir Putin signed a federal law on protection of bank deposits in Crimea and Sevastopol.
Putin also appointed a new deputy commander of Russia's naval forces in the Black Sea. Putin named former Ukrainian Navy Commander Admiral Denis Berezovsky to be the new deputy commander of the Russian Black Sea Fleet.
Putin also signed a decree rehabilitating Crimean Tatars and other peoples who were the target of Stalin-era repression.
Putin's decree is seen as an attempt to win support from non-Russian minority groups on the Crimean Peninsula.
Based on reporting by Reuters and AFP