EU foreign policy Chief Federica Mogherini was "extremely worried" as the situation with the Belgrade-Mitrovica train "could have escalated."

Mogherini said this on Monday afternoon while addressing reporters after a meeting of EU foreign ministers in Brussels.

She was asked to comment "on the tensions over the weekend between Belgrade and Pristina over the 'train problem'," and "the involvement of the two sides" as well as "the nature of the (EU-facilitated Belgrade-Pristina dialogue at this moment and how it will continue in the future."

"I was personally not only following the issue of the train over the weekend, but was also personally in touch," she said, adding that she was in contact with Serbian Prime Minister Aleksandar Vučić over Saturday's incident when special Kosovo police prevented the train from reaching its destination – and was "extremely worried about the situation that could have easily escalated."

"My message to both sides was to avoid escalation, avoiding moves and messages and to seek to jointly engage in a dialogue, so this brings the results for both sides. Not just for the institutions on both sides, but for the people."

She said that the steps that the EU realized together with Belgrade and Pristina last year, "in some way were historical."

"We have succeeded in doing that, to progress faster and more in a perspective towards the European Union, and of the entire region," said Mogherini.

"This sometimes requires political courage, I know that very well, political will and leadership, political vision and we helped in it, but when it comes to further dialogue, it is a question for Belgrade and Pristina," said Mogherini.

She added that she saw "on both sides" determination to continue.

"That sometimes means that they have to make difficult decisions and choices, and for which well has been known a pledge, from a good reasons for both sides, but the work and commitment that I see, and in Belgrade and Pristina are powerful," said Mogherini.

"Allow me to thank the Prime Minister Vučić for the leadership role he has showed in difficult times," said the High Representative of the EU, adding that "and I think this provides a good basis for him to persist in what he is doing for the country, the people and for the dialogue in the region."