U.S. Secretary of State Condoleezza Rice and her Czech counterpart Karel Schwarzenberg signed in Prague on Tuesday a missile shield treaty despite protests from the Czech public and Russia, and she called it a key treaty of 21st century.

U.S. Secretary of State Condoleezza Rice (L) and her Czech counterpart Karel Schwarzenberg sign the main treaty on the stationing of a U.S. radar base on Czech soil in Prague July 8, 2008. (Xinhua/Ceteka)

Rice said the signature of the main treaty on the stationing of a U.S. radar base on Czech soil is important not only for the United States and the Czech Republic, but also for NATO and the whole international community.

She emphasized that the threat of a missile attack is not " imaginary" as Iran continues enriching uranium.

The document signed on Tuesday is a key treaty of the 21st century, she said, adding that it unites friends and allies faced with the same risk.

The planned U.S. radar base on Czech soil will be useful even by itself, Rice said after signing the treaty on the radar with Schwarzenberg.