The United States has called on Serbia to withdraw its forces from the border with Kosovo following a significant military build-up. The White House has detected an “unprecedented” staging of advanced Serbian artillery, tanks, and mechanized infantry units near the frontier after deadly clashes erupted at a monastery in northern Kosovo. The violence, which resulted in the death of a Kosovar police officer and three Serb gunmen, marks a severe escalation in tensions between Serbia and Kosovo.

White House National Security Council spokesman John Kirby expressed concern over the Serbian military deployment, describing it as a "very destabilizing development." The purpose of the build-up is still unclear, but Secretary of State Antony Blinken has urged Serbian President Aleksandar Vucic to de-escalate the situation and return to dialogue. Similarly, White House national security adviser Jake Sullivan has spoken with Kosovo's prime minister to address the ongoing crisis.

While Vucic did not deny the recent military build-up, he rejected claims that his country's forces were on high alert. He stated that the combat readiness of Serbian forces had not reached the highest level and emphasized that Serbia has fewer troops than it did two or three months ago.

The clashes that triggered the tensions occurred when heavily armed Serb gunmen ambushed a patrol near the Serbian border, resulting in the death of a Kosovo police officer. Following the initial attack, several assailants barricaded themselves at an Orthodox monastery, leading to an intense firefight where three gunmen were killed and three were arrested. Kosovo's government has accused Belgrade of supporting the entire operation. A member of a major Kosovo Serb political party has admitted to leading the gunmen, according to his lawyer.

The attack was characterized by a "very high level of sophistication," involving approximately 20 vehicles and “military-grade” weapons and equipment, according to Kirby. The international community has expressed growing concern over the situation.

In response to the escalating tensions, NATO has authorized the bolstering of forces for Kosovo. The alliance's peacekeeping force, known as KFOR, is expected to increase its presence in the region. NATO Chief Jens Stoltenberg has confirmed that the U.S.-led alliance is prepared to strengthen the force to address the current situation.

The conflict between Kosovo and Serbia dates back to the bloody war in 1998-99, with Kosovo declaring independence in 2008, a move not recognized by Belgrade and Moscow. Tensions have been particularly strained between the ethnic Albanian majority and Serb minority in northern Kosovo in recent months.