WASHINGTON - The NATO chief said on Monday that the missile shield in Europe will continue to be expanded toward full operational capability after leaders of member states meet in Chicago later this month.

The summit slated for May 20-21 will declare "an interim capability" of the system that brings the contributions from individual member countries together under NATO command and control, Anders Fogh Rasmussen wrote in The Wall Street Journal.

"This interim capability will provide the alliance with a limited but operationally meaningful and immediately available capability against a ballistic-missile threat," he wrote.

"It is the first step, but a real step, toward providing full coverage for all NATO populations, territory and forces in Europe, " he stated.

The secretary general noted that the military alliance conducted successfully its first comprehensive test of the new missile defense capability last month.

"A U.S. ship, radar and satellite, as well as interceptor batteries from Germany and the Netherlands, conducted a series of simulated engagements to test the alliance's ability to defend against missile attacks," he wrote. "The test was successful."

He called the test "a clear demonstration of transatlantic solidarity in action" as well as NATO's continuing determination to protect its members' territory and populations from attack and the threat of attack.

"After the Chicago summit, we will continue to expand the system toward full operational capability," he declared.

Among NATO members, the Netherlands has announced plans to upgrade four air-defense frigates with missile-defense radar, France plans to develop an early-warning capability and long-range radar, and Germany has offered Patriot missile batteries and is hosting the NATO command-and-control at Headquarters Alliance Air Command in Ramstein, Rasmussen noted.

"Turkey, Romania, Poland and Spain have all agreed to host U.S. assets. I expect more announcements in the months and years ahead," he wrote.

The missile shield was agreed on in November 2010 when the NATO leaders last met in Lisbon, Portugal to guard against threats from countries like Iran.

Russia and NATO agreed then to seek ways to cooperate on the system but have failed so far to reach a deal. Moscow wants a legally binding guarantee that the system will not be used against Russia, while Washington says it cannot agree to any formal limits on missile defense.

Russia warned again this month that it might use "destructive force" pre-emptively to take out elements of the missile shield.