Ukraine's president signed a decree on Tuesday to boost his armed forces by 100,000 troops over three years, as European leaders lined up to back him in a standoff with Russia and the United States demanded immediate Russian de-escalation.
President Volodymyr Zelenskiy urged lawmakers to stay calm and avoid panic, saying he had ordered the increase "not because we will soon have a war... but so that soon and in the future there will be peace in Ukraine".
Russia has massed more than 100,000 troops near Ukraine's borders. It denies plans to invade but says it could take unspecified military action if demands are not met, including barring Ukraine from ever joining NATO. The United States and its allies say any invasion would trigger tough sanctions.
Speaking to Russian Foreign Minister Sergei Lavrov by phone, U.S. Secretary of State Antony Blinken reiterated Washington's readiness to continue dialogue, but called for "immediate Russian de-escalation and the withdrawal of troops and equipment from Ukraine's borders", the State Department said.
Ukraine's armed forces number about 250,000, compared to Russia's overall strength of around 900,000.
Russian troops have been holding drills in Belarus and in a breakaway region of Moldova, potentially making it possible to attack from several directions.
Ukraine said it was working with Poland and Britain to strengthen cooperation "in the context of ongoing Russian aggression".
On a visit to Kyiv, Polish Prime Minister Mateusz Morawiecki said Warsaw would help Ukraine with gas and arms supplies, as well as humanitarian and economic aid.
"Living close to a neighbour like Russia, we have the feeling of living at the foot of a volcano," said Morawiecki, promising Ukraine artillery ammunition, mortar bombs, portable air-defence systems and surveillance drones.
British Prime Minister Boris Johnson also visited Kyiv on Tuesday in a Western show of support intended to convince Russian President Vladimir Putin he would pay a high price for any aggression.
"We urge Russia to step back and engage in dialogue to find a diplomatic resolution and avoid further bloodshed," Johnson said in remarks released ahead of his arrival.
Some countries have removed non-essential embassy staff from Kyiv and Washington advised on Tuesday against travel to Belarus because of "an increase in unusual and concerning Russian military activity near the border with Ukraine."
The West last week formally rejected Russian demands to bar Ukraine from ever joining NATO and pull out NATO forces from eastern Europe. Western countries say they are still willing to talk about arms control and confidence-building measures.
Russia has not yet signalled its next move, and the Kremlin reiterated that Putin would respond "when he considers it necessary".
Putin said last week the United States and NATO had not addressed Moscow's main security demands but Russia was ready to keep talking.
He spoke on Tuesday by phone to Italian Prime Minister Mario Draghi, whose office said the two leaders agreed on the need to find a "sustainable and durable" solution to the crisis and to rebuild a "climate of mutual confidence".
Draghi highlighted the importance of reducing tensions in Ukraine "in the light of the serious consequences that a further escalation of the crisis would have", his office said.
Europe's dependence on Russian energy supplies weakens the West's hand in responding to any invasion with sanctions. The United States and EU already imposed several rounds of sanctions that had little impact on Russia's behaviour since 2014, when Moscow seized Ukraine's Crimea peninsula and backed a separatist uprising in eastern Ukraine.
In recent weeks, Washington has asked major gas producers to study if they can supply extra gas to Europe if Russian flows are disrupted. The minister of state for energy of one of the biggest, Qatar, said on Tuesday it would not be able to unilaterally replace Europe's energy needs.
Washington says it has received a written follow-up from Russia on the security demands Moscow has set out.
A senior diplomatic source told Russian news agency RIA the letter contained questions from Lavrov, also sent to other NATO members, on how Moscow's counterparts understood the notion of "indivisibility of security".
Moscow SAYS NATO's addition of 14 new members in eastern Europe since the Cold War poses a threat to Russia, and that NATO is violating an agreed international principle that countries should not strengthen their own security at the expense of others.