Norwegian air force F-16 fighters patrol over the Baltics during a NATO air-policing mission. Thomson Reuters OSLO (Reuters) - Norway, which shares an Arctic border with Russia, lacks a "credible plan" how to meet NATO's spending target, US President Donald Trump said in a letter to the country's prime minister, the Norwegian daily VG reported on Tuesday.

Oil-rich Norway has committed to buy more than 50 F-35 fighter jets from Lockheed Martin as part of efforts to beef up its air forces, and contributed troops to NATO's mission in the Baltics, but Norway should do more, Trump was quoted as saying.

"Norway ... remains the only NATO ally sharing a border with Russia that lacks a credible plan to spend 2 percent of its gross domestic product on defense," Trump said in the June 19 letter, a copy of which was published on VG's website.

He said he expected to see "a strong commitment" from Norway, what he called the Alliance's "eyes and ears" on the northern flank, at the NATO summit in July.

This year, Norway plans to spend 1.56% of gross domestic product, down from 1.62% in 2017.

Marine Corps Commandant Gen. Robert B. Neller, left, speaks with a Norwegian army soldier in Setermoen, Norway, September 28, 2017. (US Marine Corps/Cpl. Samantha K. Braun)

Norwegian Prime Minister Erna Solberg told a regular new conference on Tuesday the country aimed to strive toward the 2 percent target, reiterating the government's position and without providing any deadlines.

"We will stop the decline ... and we will move towards 2% by 2024," Solberg later told Norwegian broadcaster NRK, referring to Trump's letter.

Norway, like Germany, maintains that it is important to move toward the 2% target, but it has never pledged to reach it by 2024. Other countries, such as Spain and Hungary, have previously said that they would miss the deadline.

Norway says it is the second biggest spender per capita on defense after the United States in NATO.

The US Embassy in Oslo was not immediately available to comment on the letter. Trump said last month that NATO members that do not contribute fully to the group would be "dealt with."

(Reporting by Nerijus Adomaitis; editing by Alison Williams)