In a letter to his NATO counterparts before the meeting, Ukrainian Foreign Minister Andrii Sybiha said an invitation would remove one of Russia's main arguments for waging its war - namely, preventing Ukraine joining the alliance.
But there is no sign of the required consensus among NATO's 32 members for such a decision at the foreign ministers' meeting in Brussels, said diplomats, speaking on condition of anonymity.
Previewing the meeting, NATO Secretary-General Mark Rutte said on Tuesday the alliance was working on "building the bridge" to membership for Ukraine.
But he said the most urgent issue was providing Kyiv with more arms to repel Russian forces.
NATO Secretary-General Mark Rutte welcomed recent announcements of more military aid for Ukraine. (AP PHOTO)
"The meeting in the next two days will very much concentrate on how to make sure that Ukraine, whenever it decides to enter into peace talks, will do so from positional strength," he said.
"And to get there, it is crucial that more military aid will be pumped into Ukraine."
Rutte said he welcomed recent announcements of more military aid for Ukraine by the United States, Germany, Sweden, Estonia, Lithuania and Norway.
The US on Monday announced a new weapons package for Ukraine worth $US725 million.
Ukraine's foreign ministry said on Tuesday it would not settle for anything less than NATO membership, citing its experience with a pact 30 years ago under which it relinquished nuclear arms in exchange for security assurances from major powers that never materialised.
"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," the ministry said in a statement.
Ukraine sees NATO membership as the best guarantee of its future security.
Under NATO's Article 5 mutual defence pact, members agree to treat an attack on one as an attack on all and come to each other's aid.
German Chancellor Olaf Scholz was the latest NATO member to visit President Volodymyr Zelenskiy. (AP PHOTO)
Ukrainian President Volodymyr Zelenskiy suggested on Friday in a Sky News interview that putting territory currently controlled by his government "under the NATO umbrella" would stop the "hot phase" of the war.
His comments came as Ukraine faces a tough winter on the battlefield, with Moscow's troops advancing in the east and Russian air strikes targeting the country's hobbled energy grid.
While NATO has declared Ukraine will join its ranks and that the country's path to NATO is "irreversible", it has not issued an invitation or set out a timeline for membership.
Any such decision would depend above all on NATO's predominant power, the United States, so will soon be a matter for Trump, when he returns as US president in January.
Trump has criticised the scale of US aid for Kyiv and said he will end the war in a day.
But he has not set out a detailed plan of how he will tackle the conflict.
Some NATO members, such as Hungary, have openly voiced opposition to Ukraine joining the alliance.
Some others, including the current US and German governments, have signalled they do not think the time is right, diplomats say.
