Robert F. Simmons Jr., a Foreign Service officer who most recently served as senior adviser in the Office of South Central European Affairs, died Dec. 24 at his home in Rochester, N.Y. He was 63. He also had a residence in Washington.

The cause was a heart attack, said his brother, Edward Simmons.

Mr. Simmons joined the Foreign Service 1972 shortly after graduating from Georgetown University’s School of Foreign Service.

From 2003 to 2011, he served on the international staff of NATO in Brussels as deputy assistant secretary general for security, cooperation and partnership. He had served at the U.S. Embassy in Islamabad, Pakistan, and been a senior arms control and disarmament negotiator.

Robert Francis Simmons Jr. was born in Rochester. He received a master’s degree from the Johns Hopkins School for Advanced International Studies in 1974.

Survivors include a brother and two sisters.

— Bart Barnes