Sikorski, who arrived in Brussels on Tuesday to attend a meeting of NATO foreign ministers, was commenting on the 30th anniversary of the signing of the Budapest Memorandum in December 1994.

Under this agreement, the United States, Russia, and the United Kingdom pledged to uphold Ukraine’s sovereignty and territorial integrity in exchange for Kyiv relinquishing its post-Soviet strategic nuclear weapons to Moscow.

The Ukrainian Foreign Ministry marked the date with a statement, saying: “With the bitter experience of the Budapest Memorandum behind us, we will not accept any alternatives, surrogates or substitutes for Ukraine’s full membership in NATO.”

Responding to Kyiv’s comments, Sikorski said: “The main party [to the agreement] was Russia, which received probably the third-biggest nuclear arsenal in the world in exchange for guaranteeing the independence and inviolability of Ukraine’s borders."

He added: “So yes, Ukraine has the right to feel disappointed that these guarantees are not respected today.”

NATO foreign ministers have gathered in Brussels for a two-day meeting, during which Ukraine’s top diplomat is expected to push the allies to extend Kyiv a formal invitation to join the alliance.