PRISTINA, Kosovo — President Joe Biden said that Kosovo holds a “special place’ for his family because of the time his late son Beau spent in the war-torn country helping to strengthen the rule of law there.

Biden’s remark was made in a letter the U.S. president had sent to Kosovo’s acting President Vjosa Osmani on the occasion of the country’s independence day. Osmani made the contents of the letter public on Tuesday.

Kosovo declared independence from Serbia in Feb. 17, 2008, a decade after a brutal 1998-1999 war between separatist ethnic Albanian rebels and Serb forces. The war ended after a 78-day NATO air campaign drove Serb troops out and a peacekeeping force moved in.

“Kosovo continues to hold a special place for the Biden family in honor of the time our late son Beau Biden spent working to ensure peace, justice and the rule of law for all the people of Kosovo,” Biden wrote.

Beau Biden worked in Kosovo after the 1998-1999 war with the military forces and also with the Organization for Security and Cooperation in Europe strengthening the rule of law there.

Biden visited Kosovo in 2016 on his last trip to the region as vice president to attend with his family a ceremony naming a road near an American military base after his son who died a year earlier of brain cancer at age 46.

In the letter, Biden also urged for “a comprehensive normalization agreement with Serbia centered on mutual recognition.” Biden urged the same in a letter to Serbia’s President Aleksandar Vucic earlier this month.

Most Western nations have recognized Kosovo, but Serbia and its allies Russia and China do not. Tensions over Kosovo remain a source of volatility in the Balkans.