NATO's chief on Monday expressed the Western alliance's determination to move ahead with building an operational missile defense system, following what he called its first successful comprehensive test.

After a NATO summit in Chicago later this month, "we will continue to expand the system toward full operational capability," NATO Secretary General Anders Fogh Rasmussen wrote in an op-ed piece in The Wall Street Journal.

"The alliance has already developed an initial command-and-control system to link the US assets with sensors and interceptors provided by European allies," Rasmussen pointed out.

"I expect more announcements in the months and years ahead."

NATO leaders are hoping to declare the start of an "interim capability" for the missile shield at the summit in Chicago on May 20-21.

According to Rasmussen, this "interim capability" will provide the alliance with a limited but operationally meaningful and immediately available capability against a ballistic-missile threat.

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

However, the alliance and Russia have failed to reach a compromise on the system, which Russia fears would thwart its nuclear deterrent despite NATO assurances that it is aimed at Iran and other threats.

Moscow has demanded legally-binding guarantees that the missile shield will not undermine its arsenal, but NATO refuses to enter into such an agreement and has instead offered political reassurances.

Ratcheting up the heat, Russia warned this month that it might have to deploy new missiles in Europe to potentially take out elements of the controversial shield.

Russian Chief of Staff General Nikolai Makarov said one option was for Russia to station short-range Iskander missiles in its Kaliningrad enclave near Poland.

Rasmussen did not comment of Moscow's threats.

But he announced that last month NATO conducted the first comprehensive test of the missile-defense capability, during which US 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 said the test was successful.

"The test was a clear demonstration of trans-Atlantic solidarity in action," said the NATO chief. "It also shows NATO's continuing determination to protect our members' territory and populations from attack and the threat of attack."

The first elements of the US network of satellites, sensors and sea-based interceptors are already deployed to Europe, Rasmussen said.

The Netherlands has announced plans to upgrade four air-defense frigates with missile-defense radar, while France, according to the NATO chief, plans to develop an early-warning capability and long-range radar.

Germany has offered Patriot missile batteries and is hosting the NATO command-and-control at Headquarters Alliance Air Command in Ramstein.

Meanwhile, Turkey, Romania, Poland and Spain have all agreed to host US assets, Rasmussen pointed out.