"Gen. Mattis has been known for being a strong supporter of transatlantic relations, NATO and allied relations," Ms Kaljurand told ERR. "And if you also consider the fact that Gen. [John] Kelly is also leaving at the end of the year, then two especially sensible people who understand international relations are leaving the Trump administration."

What will this mean for Estonia? "I believe that we should wait and see who will be made the next defence secretary, and then we can discuss it further," Ms Kaljurand continued. "But my initial reaction is that I am sad. I'm definitely disappointed, and Gen. Mattis is well known in Estonia. So yes, we are losing a very strong ally and friend."

Mr Kallas, meanwhile, stressed that the defence secretary of the US is one of the most important figures in security policy.

"Mattis embodied traditional American security policy, which meshed well with our understanding of global security," he said. "His departure will certainly create quite a bit of uncertainty."

According to Mr Kallas, there are those who will rejoice over Mr Mattis' departure, and those who are worried and thinking about what will happen now. "We are definitely among those who are thinkin, 'What will happen now?'"

At the same time, he didn't believe that a new defence secretary in the US could mean any kind of very big or radical changes.

"While the commander-in-chief is of course the president, defence policy, the [Armed Forces] and security policy are all such a large phenomenon that they cannot very suddenly steer it in one direction or another," Mr Kallas added.

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