In a phone call with Russian Foreign Minister Sergei Lavrov concern John Kerry "deep about the lack of positive Russian steps".
Russia accused Kiev Guide for the collapse of last week Heskem.
President of Ukraine ordered before the relaunch of the military operations against pro-Russian fighters in the East of the country.
It came as President Oleksandr Turchynov said, that two men - including municipal politician Vladimir Rybak - after "brutally tortured" have been found dead.
"The terrorists, who effectively took the entire region Donetsk hostage now gone too far," he said.
Politician Vladimir Rybak disappeared after filmed a building of pro-Russian activists tried to access seized, as Daniel Sandford reportsSeparatists in the Eastern Ukraine, throw back with undercover military Russia the United States and the West, where public buildings in at least nine towns and cities are occupied. Russia denied involvement.
In other developments:
Some 150 American troops come in Poland, which is the first part of a 600-strong deployment, saying Washington supposedly American journalist Simon Ostrovsky a demonstration of strength for the NATO allies in the RegionPro Russian fighter in Slavyansk, works hold for Vice news. "Lack of progress"In his conversation with Mr Lavrov on Tuesday Mr Kerry "urged Russia rhetoric, disarm sound engage diplomatically in the East... and issue public statements for those buildings," after a senior official of the Ministry of Foreign Affairs.
"Secretary Kerry also confirms that the lack of measurable progress in the implementation of the Geneva agreement will lead reinforced sanctions against Russia," the official said.
The warning came after US Vice President Joe Biden met Ukrainian new leaders in Kiev and Russia calls to "Stop talking and start to act" to defuse the crisis in the Ukraine.
A visit to Kiev, Mr Biden warned on Russia to "provocative behavior" would result in "greater isolation" armed masked a volley at the funeral for one of the three per Russia fired fighters killed at a checkpoint on SundayThe United States m (£30 m) for the political is an additional $50 and helping economic reforms in Ukraine, including $11 m to run the presidential election on May 25 due.
Read the main story Steve Rosenberg BBC News, SlavyanskIn the Church of the Holy Spirit in the Centre of Slavyansk, an Orthodox priest called prayers for the dead. The bodies of three pro-Russian activists, shot dead at a temporary checkpoint on Easter Sunday, lay in open coffins.
When the coffins from the Church, the crowd shouted outside "Fame the heroes of Donbass!" over and over again - Donbass is the name for the Don basin. Church bells rang out.
The people who I talked to here are convinced that it was a Ukrainian nationalist, which carried on the Sunday attack. A woman told me she was proud, Ukrainian, but this instability and violence urged people here want closer relations with Russia.
Seasoned US Washington sent 600 troops to participate in NATO exercises in the Baltic States and Poland.A Defense Department spokesman said the decision was designed to a strong commitment to the Alliance as events unfolded in the Ukraine show.
Open coffinsIn the meantime the burials of three men took place shot manned on Sunday during a RAID on a checkpoint, with pro-Russian separatists near the town of Slavyansk.
The local separatists said that the attack by the ultra-nationalist right sector Kiev called fighters but it was conducted a "provocation" staged by Russian special forces.
The bodies of those killed lay in open coffins at the funeral in the Church of the Holy Spirit in the Centre of Slavyansk.
The BBCs Daniel Sandford reports about the "uncontrolled sorrow" at the funerals of pro-Russian activists in SlavyanskAnnouncing the decision to reactivate the military operation in the East of Ukraine, Mr Turchynov said in a statement: "I should call the security authorities which continue and implementation of successful anti-terror measures, to the defense of Ukrainian citizens living in the East of Ukraine against terrorists."
Kiev military operation that will end occupation of buildings began on April 16 but was suspended over the Easter period.
Mr Rybak, whose Leiche was found on Tuesday near the town of Slavyansk, was described as a municipal councilor for the fatherland party in the nearby town of Horlivka. The other man was killed is still not publicly identified.
Mr Rybak had missed recently, and according to the police, his body was found in a river.
"This crime with the full support and acquiescence of the Russian Federation are committed," said Mr Turchynov.
Public buildings in at least nine cities and towns remain occupiedIn another incident a Ukrainian military reconnaissance aircraft by small arms fire over Eastern Ukraine on Tuesday met the Ministry of defence said.
The plane, an Antonov to-30, suffered minor damage on Slavyansk as it was by automatic gunfire, target according to the Ministry. No one was injured and the plane safely back to Kiev.
The United States have previous said it plans, Russia should not be further sanctions, to meet its Geneva obligations.
17 April Geneva Accord in accordance with an immediate end to the violence in the East of Ukraine and urges the illegal armed groups surrender their weapons and public buildings.
But Russian Prime Minister Dmitry Medvedev said the Russian Parliament on Tuesday, the Russia capable of, to "minimize the impact" further sanctions.
Ukraine has in November last year in turmoil since when Kiev was gripped by protests, whether the country should lean more towards Russia or Europe.
Are you in the Eastern Ukraine? How has you concerned the unrest? You can email your experiences at haveyoursay@bbc.co.uk, with the subject line 'Ukraine'.