BRUSSELS — The head of NATO called today for the U.S., Russia and NATO to link their missile defense systems against potential new nuclear threats from Asia and the Middle East, saying the old foes must forget their lingering Cold War animosity.

Secretary-General Anders Fogh Rasmussen appealed for unity a day after the U.S. shelved a Bush-era plan for an Eastern European missile defense shield that has been a major irritant to Russia.

"We should explore the potential for linking the U.S., NATO and Russia missile defense systems at an appropriate time," he said.

"Both NATO and Russia have a wealth of experience in missile defense. We should now work to combine this experience to our mutual benefit," he added.

The immediate reaction from Russia was positive. Dmitry Rogozin, Russia's envoy to NATO spoke of a "very positive tone ... Cooperation with Russia is not a matter of choice (for NATO but) of necessity."

Fogh Rasmussen said long-range ballistic missile technology in the hands of such countries as North Korea and Iran threatens the West and Russia in large part because it could lead to regional proliferation.

"The proliferation of ballistic missile technology is of concern not just to NATO nations, but to Russia too," he said.

A key irritant in NATO's relations with Moscow is the drive to bring ex-Soviet states and satellites into the alliance which now has 28 members. The membership prospects of Georgia and Ukraine especially have soured relations.