Prime Minister Rishi Sunak is being urged to raise UK defense spending by a key eastern European ally.
Estonia, which borders Russia, has hosted British troops on rotation for years.
Foreign minister Urmas Reinsalu says it was vital all Nato countries spend 3% of gross domestic product on defence.
The new prime minister has previously described such targets as "arbitrary".
He however says he believed in investing in our armed forces" during his campaign to be Tory leader over the summer.