NATO chief Jens Stoltenberg said on Thursday that it’s up to Finland and Sweden to seek membership.He added that if they want to join the military alliance, both would be quickly welcomed. Finland and Sweden offered the strongest indications that they will soon pursue NATO membership. LoadingSomething is loading.NATO Secretary General Jens Stoltenberg on Thursday said Finland and Sweden would be quickly welcomed to the military alliance if they choose to apply in the near future.”If they apply, they will be welcomed, and I also expect the process to be quick and that they can then join NATO after the formal process has been finalized,” Stoltenberg told reports in Brussels at a joint press conference with European Parliament President Roberta Metsola.Stoltenberg said it’s up to the two Nordic countries to decide if they want to apply for membership, but if they decide to do so, they “will be welcomed with open arms to NATO.” Finland and Sweden earlier this month signaled they would seek NATO membership — reportedly set to apply as soon as this summer. The two countries have historically been militarily unaligned, but Russia’s invasion of Ukraine alarmed both countries and prompted consideration of joining the international alliance. “Everything changed when Russia invaded Ukraine,” Finnish Prime Minister Sanna Marin said at a joint press conference with her Swedish counterpart Magdalena Andersson in Stockholm.Andersson said the “security landscape has completely changed,” adding that it was time to consider Sweden’s best security interest.  Russia in response threatened “serious military and political repercussions” if they joined the military alliance and said it would deploy nuclear weapons to the Baltics — despite the fact that it’s assessed Russia has already done so.   Article 5 of NATO’s charter says an attack on one member is an attack on them all — leaving Russia with the choice to attack NATO as a whole if it pursues punishment against Finland and Sweden.  Finland’s former prime minister Alexander Stubb told Insider’s Sinéad Baker that a response from Russia would likely come before membership is finalized, so Finland has actively sought security guarantees from member states in the run-up to the application process.    Stoltenberg on Thursday said Finland and Sweden are NATO’s closest partners, calling them “strong and mature democracies.””We know that their armed forces meet NATO standards — are interoperable with NATO forces,” Stoltenberg said.He added: “We train together, we exercise together, and we have also worked together with Finland, Sweden in many different missions and operations.”