A letter made public: Washington warned Pristina a year ago

The request for the abolition of the 100% tariffs on Serbian goods was very clear, as well as a warning that, until they did, relations with the Kosovo authorities would not be restored, and the possibility of reconsidering other, not only security, co-operation with Pristina was mentioned.
Given that Pristina's response to these requests was rather mild, President Trump and other senior State Department officials have repeatedly spoken on the same subject.
For the past ten days, we have witnessed new direct demands for the suspension of the taxes made by a personal envoy of the US president, Richard Grenell, and addressed to the new Kosovo government, led by Albin Kurti, but it does not give the impression that the effect is much greater than it was in the previous year, Kosovo online writes, and reminds that the introduction of the tariffs has had major consequences on the already fragile relations between Belgrade and Pristina and completely halted dialogue and attempts to reach an agreement on mutual relations.
A European Union-mediated dialogue between Serbia and Kosovo over normalizing ties stalled after the previous Kosovo government imposed the 100% taxes on Serbian goods in protest of Serbia's blockade of Kosovo in the International Red Cross and other international organizations.

Here's full transcript of the letter

"As President Trump wrote in his December 2018 letter, this is the moment of opportunity to advance Kosovo's future as a stable, prosperous and secure country by normalizing relations with Serbia and taking a key step toward integration with Europe-Atlantic institutions.
We have since expressed our concerns that certain actions, including the imposition of tariffs on Serbian and Bosnian products, could...