Grenell, who also served as the United States Ambassador to Germany and the Special Presidential Envoy for Serbia and Kosovo Peace Negotiations, went to North Mitrovica in Kosova unannounced to help de-escalate the situation there.
Grenell revealed that he has spoken to Serbian authorities, and said that he "always has hope." He had called for the release of the officers on Twitter. The EU had brought leaders of both Kosovo and Serbia to Brussels to try to negotiate and decrease tensions.
Recent clashes in May came after "Kosovo police seized local municipality buildings in northern Kosovo, where Serbs represent a majority, to install ethnic Albanian mayors who were elected in a local election in April after Serbs overwhelmingly boycotted the vote," the AP reports.
The officers were detained earlier in June, US News reports, and were charged with "illegal possession of weapons and explosive devices." After their release was secured on Monday morning, they "will be allowed to remain free pending potential further proceedings."
"In Kosovo," US News reported, "officials insisted the three had been kidnapped and demanded that Serbia be held responsible for allegedly violating Kosovo's territory. President Vlosa Osmani thanked the United States for securing the policemen’s release “after the act of aggression that Serbia did in Kosovo."
The dispute over the officers threatened peace in the region, which saw war in 1998-99 that killed more than 10,000 people. Most of those killed during that conflict were Kosovar Albanians. That war was over Serbia's crackdown against separatists in Kosovo, who are ethnic Albanians.
The US and EU recognize Kosovo's independence. Russia and China, however, have stated that they back Serbia's claim to the region.