U.S. Defense Chief Leon Panetta has warned NATO defense ministers that they can no longer count on the United States to cover financial shortfalls plaguing coalition operations in Libya and Afghanistan.

The ministers met Wednesday in Brussels to discuss the NATO mission in Libya, the war in Afghanistan, and efforts to acquire necessary resources as members face budget cuts.

In his first visit to Europe since taking over as U.S. Secretary of Defense in July, Panetta said NATO members must work more closely than ever to “pool resources” for missions. He said the Pentagon is facing $450 billion in cuts over the next 10 years, and he said additional cuts would be “devastating” to security in the United States and abroad.

Panetta said the fall of Libyan leader Moammar Gadhafi is an example of why NATO matters. Alliance warplanes continue to carry out airstrikes against Gadhafi loyalists.

NATO Secretary-General Anders Fogh Rasmussen has called the mission a “great success.” But he and Panetta say it has exposed shortcomings in surveillance, intelligence and air-to-air refueling capabilities.

Also Wednesday, Spain said it will host four U.S. Navy ships as part of a proposed NATO missile defense shield for Europe. The ships will be equipped with interceptors designed to knock incoming missiles out of the sky.

Spanish Prime Minister Jose Luis Rodriguez Zapatero said Spain is a NATO member committed to the collective defense of Europe.

The U.S.-led missile defense system will combine land- and sea-based radar and missile interceptors to counter a possible threat by Iran and North Korea. The United States originally planned to place radar and interceptors in Poland and the Czech Republic, bringing a loud protest and threats of retaliation from Russia.