Nato has no plans to send combat troops to Ukraine in the event of a Russian invasion, its chief said on Sunday.
Secretary-General Jens Stoltenberg said that the 30-member alliance would focus on “providing support”.
UK Foreign Secretary Liz Truss said it was very unlikely that British troops would be sent to Ukraine, which is not a member of the organisation.
The UK has said that it will bolster its forces in Eastern Europe as part of measures to prevent the “highly likely” scenario that Russia will invade Ukraine.
Mr Stoltenberg told the BBC that, "We have no plans to deploy Nato combat troops to Ukraine … we are focusing on providing support."
"There is a difference between being a Nato member and being a strong and highly valued partner as Ukraine. There's no doubt about that."
Russia last month made a series of demands including a promise from the West that Ukraine would not join Nato, which it regards as a threat to its security.
Nato’s members include former Soviet republics that border Russia – Latvia, Lithuania, and Estonia. Members of the alliance agree to go to another’s aid in the event of an armed attack.
Russia has called for an end to Nato military activity in Eastern Europe and for it to stop siting missiles in countries close to Russia.
On Saturday, British Prime Minister Boris Johnson said that the UK was considering doubling the number of its troops available to European allies in response to a military threat from Russia.
He also urged Russia to join talks to avoid a “reckless and catastrophic” invasion, which he said would result in tragedy for Europe.
Mr Johnson is expected to speak to Russian President Vladimir Putin and travel to Ukraine this week. The UK has more than 100 troops to provide training there.
There are also 900 British military personnel based in Estonia, and a Light Cavalry Squadron of about 150 is stationed in Poland.
Mr Johnson asked defence and security chiefs to consider further defensive military options in Europe last week.
Moscow denies planning to invade but has stationed more than 100,000 troops on its border with Ukraine.
It was accused by Ukraine of a cyber attack on Ukrainian government ministries this month.