The former Secretary General of NATO, Anders Fogh Rasmussen, said that some members of the Alliance could voluntarily send troops to Ukraine.

That scenario, he said, could play out if Kiev doesn't get assurances on a wide range of issues at the bloc's upcoming meeting in July in Vilnius, Lithuania.

Rasmussen, who is now an adviser to Ukrainian President Volodymyr Zelenskiy and worked with his predecessor Petro Poroshenko, said Kiev should be given written guarantees before NATO leaders meet next month, including intelligence sharing with the West, transfer of weapons and joint military exercises.

- If NATO cannot agree on a concrete map of the action path for Ukraine, there is a clear possibility that some countries will take independent actions, he said yesterday, reports the Guardian.

According to Rasmussen, Poland could be one of those countries.

- I think that the Poles would seriously consider entering the country and forming a coalition of volunteers if Ukraine does not get anything in Vilnius, he said.

Rasmussen, after a trip to Europe and the United States, during which he tried to boost military support for Ukraine, argued that, if Kiev requested it, the deployment of foreign troops to Ukraine would be in accordance with international law.

The current Secretary General of NATO, Jens Stoltenberg, recently confirmed that a certain level of security guarantees for Ukraine will be considered in Vilnius, but emphasized that full guarantees can only be offered to members of the Alliance.

The alliance first promised to grant membership to Ukraine back in 2008, and Kiev formally applied to join in September last year, although the issue of Ukraine's membership in the alliance has not advanced significantly since then.

Several NATO members have become staunch supporters of Ukraine's membership in the bloc and are calling on other Western countries to define a clear path for Kyiv to membership.

The group of Eastern European members known as the "Bucharest Nine" issued a statement two days ago from Bratislava in which they called on NATO in Vilnius "to start a new political route that will lead to Ukraine's membership in the Alliance" and to commit to "a more robust, multi-year and a comprehensive package of support for Kyiv".

Although Washington repeatedly affirms that Ukraine will one day join the Alliance, the US is currently paying more attention to the current conflict with Russia, hoping to resolve the issue of Kiev's membership later.

However, the US ambassador to NATO, Julianne Smith, told the Guardian yesterday that officials were now "considering a range of options to signal Ukraine's progress in relations with NATO", although she did not specify what that might mean.