Dutch, Estonian, Latvian and Lithuanian counterparts met in The Hague to coordinate "crucial" topics ahead of the 32-member states gathering in June, and to strengthen cooperation along the alliance's eastern flank with Russia.

"For the upcoming NATO summit in The Hague we (Lithuania) advocate that three percent of GDP for investment is the bottom line," Defence Minister Dovile Sakaliene said.

"And that should be the bottom line for everyone," she told reporters.

The NATO summit in The Hague "could be historical... and we've already seen and heard the messages coming from President-elect Trump," added Estonian Defence Minister Hanno Pevkur.

"It doesn't matter what the final agreement or decision will be made in The Hague. We all understand that two percent is not enough," he said.

The transatlantic alliance's 32 countries in 2023 set a minimum level for defence spending of two percent of gross domestic product, and Russia's war in Ukraine has jolted NATO to strengthen its eastern flank and ramp up spending.

- Increasings calls -

The call at the meeting of the four ministers in the Dutch city came against the backdrop of similar sentiments by Finland's President Alexander Stubb, who said Wednesday that Europe had to boost its military contributions.

Incoming US president Donald Trump last week said he wanted the bloc's members to up spending to five percent of GDP. And NATO chief Mark Rutte last month called for an increase, saying "we are going to need a lot more than two percent".

Dutch Foreign Minister Ruben Brekelmans, hosting the meeting, said however it was easy to "name a percentage" but the number could be more difficult to achieve.

"Given that the Russian threat is so imminent it's not only about fixing a percentage, because that's easy," said Brekelmans.

"You also need to think about if such a percentage is agreed at The Hague summit, what are we going to do the day after and how are we going to work towards that percentage," he said.

Brekelmans said he expected the "real" talks around defence norms only to happen in the final months and weeks before the summit.

At least 23 NATO countries last year hit the NATO target of two percent.