During Ukrainian President Volodymyr Zelenskyy's brief visit to Portugal, the last stop of his tour of several European countries, the two sides signed a 10-year bilateral cooperation agreement in security.

Portugal will provide Ukraine with at least 126 million euros ($137 million) this year for the "reconstruction of Ukraine," according to an agreement signed between Portugal and Ukraine on Tuesday.

"Our unwavering commitment will be maintained throughout the duration of this agreement," said Portuguese Prime Minister Luis Montenegro, assuring Zelenskyy that assistance will be provided over the next 10 years.

Fifteen EU countries and NATO have contributed more than 1.6 billion euros ($1.74 billion) to a Czech initiative to buy ammunition for Ukraine in non-EU countries, Czech Prime Minister Petr Fiala said on Tuesday.

The first tens of thousands of 155mm artillery shells will be delivered to Ukraine in June, with the first shipment expected in the coming days, Fiala said before a working dinner for security cooperation with leaders of several EU countries and Ukraine's Prime Minister Denys Shmyhal.

Russia said it will continue its special military operation in Ukraine even if Western countries step up their military presence there, Kremlin spokesman Dmitry Peskov said on Tuesday.

"There are hot heads in Western countries who are making absolutely irresponsible provocative statements," the Russian presidential spokesman said, adding that Russia regards the assertions by some Western countries as hostile actions.

NATO Secretary General Jens Stoltenberg told The Economist that alliance members should let Ukraine strike deep into Russia with Western weapons, while the White House ruled out such a possibility for U.S.-supplied weapons. "There's no change to our policy at this point. We don't encourage or enable the use of U.S.-supplied weapons to strike inside Russia," said John Kirby, White House National Security Council spokesperson.

Russian President Vladimir Putin warned the West on Tuesday that NATO members in Europe were playing with fire by proposing to let Ukraine use Western weapons to strike deep inside Russia, which he said could trigger a global conflict.

Speaking of NATO members in Europe, Putin said that small countries there "should be aware of what they are playing with," as they had small land areas and very dense populations.

"This is a factor that they should keep in mind before talking about striking deep into Russian territory," Putin said.

(With input from agencies)