"We don't plan to have an additional presence in either country, they have formidable national forces. They're capable of defending themselves," Deputy Secretary General Mircea Geoana said in a telephone interview.

Russian President Vladimir Putin warned last week that "if military contingents and military infrastructure were deployed there, we would be obliged to respond symmetrically and raise the same threats for those territories where threats have arisen for us".

Geoana said that "we don't plan to have NATO bases in these two countries, because they have a very high level of military and strategic maturity".

After the accession process was launched Tuesday, it is up to parliaments in all 30 member states to ratify Oslo and Helsinki's membership of the Atlantic alliance.

Although a deal has been struck in principle with Turkey to overcome its objections relating to the Nordic countries' policy towards Kurdish militants, there is still some suspense on whether Ankara will ratify immediately.

"We hope the process will be completed quickly," Geoana said, saying "many countries have already launched" steps towards ratification -- although he declined to lay out a precise timetable.

Also speaking Tuesday, NATO Secretary General Jens Stoltenberg said: "I count on allies to deliver a quick and swift and smooth ratification process."

Geoana hailed NATO members' and allies' support for Ukraine as it defends itself against the Russian invasion launched on February 24.

But he acknowledged "active concerns" about how long the flow of arms and ammunition can be kept up.

Although information exchange about Ukraine's needs "is working very well... there is of course the problem of reserves in allied countries," Geoana said.

Military stocks are limited in European countries, many of which lack the industrial capacity to quickly ramp up arms production for the long haul.

But "there is an effort to boost capacity and creativity from the manufacturers, it's been working very well so far," Geoana said -- recalling also that Western leaders have repeatedly stated a determination to support Ukraine for the duration.

"Everyone was aware that we'll have strategic patience" at June's NATO summit in Madrid, he added.

But as the fallout from the war hits energy, food and financial markets, observers have warned that national leaders may face growing public opinion and funding constraints.