The United States and Japan will soon announce an agreement aimed at breaking a long deadlock on a military base in Okinawa, a senior US official said Thursday.

Kurt Campbell, the assistant secretary of state for East Asia, said the two countries would release a "breakthrough" and "very specific" deal at 0200 GMT Friday.

"It breaks a long stalemate on Okinawa," Campbell said at the Center for Strategic and International Studies, a Washington think tank.

Campbell said the deal would be "very specific" on troop levels and entail the return of land in Okinawa, where tensions have long been rife with the US troops due to the large military presence.

The deal comes just before Japan's Prime Minister Yoshihiko Noda holds a summit on Monday with President Barack Obama in Washington.

Three leading US senators had earlier raised objections over the pending base deal, saying in part that it was unclear on financing, but Campbell said he believed their concerns have been addressed.