The White House says U.S. Vice President Mike Pence has encouraged Kosovo to ratify a border-demarcation deal with Montenegro.
Pence met with Kosovo President Hashim Thaci in Washington on September 29, two days after Kosovo's new prime minister said the Balkan state had no deadline for resolving the border standoff, which the European Union insists Pristina must approve before its citizens can travel visa-free within the Schengen zone.
In addition to calling for a resolution to this "long-standing issue," Pence reaffirmed U.S. support "for a sovereign, democratic, and prosperous Kosovo," the White House said in a statement.
It added that Pence expressed appreciation for efforts by Thaci and Serbian President Aleksandar Vucic to advance normalization between Belgrade and Pristina under an EU-facilitated dialogue.
Kosovo declared independence from Serbia in 2008 and is recognized by 115 countries, but not by Belgrade.
The European Union has urged Pristina and Belgrade -- both seeking to join the EU -- to normalize relations and is sponsoring talks aimed at ending years of hostility.
In a Facebook post following the White House meeting, Thaci called the United States a "guarantor of independence" for Kosovo and a "powerful" advocate for Kosovo's accession to the EU and NATO.
Thaci in March backed away from a controversial vow to push through a law turning the country's security force into a national army after meeting resistance from the United States and NATO.
The White House said in its statement that Pence expressed support for the transformation of NATO-trained security forces "via constitutional means."
Kosovo has a substantial ethnic Serb minority, and the draft law Thaci had sent to parliament -- unlike constitutional amendments -- would not have required voting approval from Kosovo's ethnic minorities.
The United States and NATO warned earlier that they would reduce military cooperation if Kosovo transformed its NATO-trained security forces into a regular army without consulting all groups.
The White House added that Pence and Thaci "agreed on the importance of advancing reforms to strengthen the rule of law, fight corruption, and boost economic growth."
With reporting by RFE/RL's Balkan Service, AP, and RTK