U.S nuclear expert in Kashmir entourage

James Ellis (pictured in 1998)

BRUSSELS, Belgium (CNN) -- A senior military official with detailed knowledge of India and Pakistan's nuclear weapons will accompany U.S. Defense Secretary Donald Rumsfeld during his meetings with the two countries' heads of state next week, a U.S. official told CNN Thursday.

Rumsfeld is in Brussels Thursday meeting with NATO allies ahead of his visit next week to India and Pakistan in an attempt to diffuse tensions between the two nuclear neighbors.

Adm. James Ellis, Commander in Chief of the U.S. Strategic Command, will sit in on Rumsfeld's meetings with Indian Prime Minister Atal Behari Vajpayee and Pakistan's president, Gen. Pervez Musharraf.

Ellis is expected to warn both India and Pakistan that they cannot conduct a limited conflict without risking a full-scale nuclear exchange, sources told CNN.

As head of strategic command, Ellis is the senior U.S. military official with detailed operational knowledge of U.S. and foreign nuclear weapons.

Ahead of Rumsfeld's visit, Deputy Secretary of State Richard Armitage met with Pakistani officials in Islamabad Thursday and is scheduled to visit India on Friday.

The nuclear rivals have massed about a million troops along Kashmir's Line of Control raising international fears of a possible nuclear war developing from the dispute over Kashmir, which already has sparked two wars between Pakistan and India.