Russia’s attack on Ukraine “is still very likely”, but the humanitarian cost “will be huge,” said US President Joe Biden.
In a nationwide televised address, Mr Biden said the United States was ready to respond immediately.
The US president has said that Russia now has an army of 150,000 troops on its border with Ukraine.
Russia’s defense minister has said some troops have left. Mr Biden said that had not been confirmed.
“[The departure of Russian troops] will be fine, but we have not yet made sure of that. We have not made sure that the Russian military returns to its home strongholds,” the US president said. “In fact, our assessment shows that they are still in a terrible position.”
Biden’s speech comes hours after Russian President Vladimir Putin said Russia’s security concerns should be addressed and taken seriously.
Mr Putin has always denied that he is planning an attack, and said Russia does not want another war in Europe. However, tensions have been rising since December.
Russia has a long and historic relationship with Ukraine, which is a former Soviet republic.
Mr Putin wants assurances that he will not join the Western military alliance-Nato, because he sees any expansion of Nato territories as a threat to Russia. Nato has denied the allegations.
Mr Biden said he agreed with the Russian government’s proposal to continue diplomacy.
The US president has also warned that the US economy could be disrupted – due to energy supply and inflation in the event that sanctions are imposed against Russia in response to any Ukrainian invasion.
“The American people understand how to protect democracy and freedom and have never been achieved without cost,” the US president said. “I will not be deceived that this will not cause pain.”
He said that the administration is making efforts to prepare plans with energy producers and distributors to eliminate the possibility of a power supply problem.
Mr Biden warned that Russia’s proposal for a pipeline to build a Nord Stream 2 gas pipeline to Europe “would not be implemented” if Ukraine’s invasion continued.
The US president went on to say: “To the Russian people: you are not our enemies, and I do not believe you want a bloody, destructive war against Ukraine.”
Nato described “having little faith” on Tuesday in connection with the announcement by the Russian military that it had withdrawn some of its troops from the country’s border with Ukraine.
US Secretary of State Antony Blinken told his Russian counterpart Sergei Lavrov in a telephone conversation that the United States needed to see “guaranteed, reliable and meaningful withdrawal of forces”.
Earlier, British Prime Minister Boris Johnson sent a Twitter message that there were “mixed signs” from Russia, because British intelligence showed Russian emergency hospitals were being built near the border that “could only be built in preparation for the invasion. “.
Vladimir Putin said earlier on Tuesday that Russia does not want war. He spoke after a four-hour conversation with German chancellor Olaf Scholz.
The Russian president told reporters in Moscow: “Do we want this or not? Of course not. That is why we are putting forward proposals for the negotiation process.”
Mr Putin also said that Nato had so far failed to address Russia’s “fundamental” security concerns. He claims that Ukraine’s issue of joining Nato should be resolved now – even though Ukraine still has a long way to go to start applying to join the alliance.
Mr Scholz said at a joint press conference that the increase in Russian troops was “unacceptable”, but added that there was still a chance that diplomatic solutions could reduce tensions.
“I explained that the increase in the number of troops is seen as a threat,” Mr Scholz said in an interview with reporters.
