The United States and the Czech Republic signed a treaty on Tuesday allowing Washington to build part of a missile defence shield in the central European state despite opposition from its former Cold War master Russia.

The deal to create a radar station southwest of Prague was marred by a failure to seal a corresponding pact with Poland, where Washington wants to put 10 interceptor rockets that would be guided by the Czech site.

Washington says the shield would defend it and its European allies against missile attacks from a foe such as Iran, and points to intelligence suggesting Tehran could develop a long-range missile capable of striking its soil by 2015.

"We face with the Iranians, and so do our allies and friends, a growing missile threat that is getting ever longer and ever deeper, and where the Iranian appetite for nuclear technology . is still unchecked," U.S. Secretary of State Condoleezza Rice said in Prague.

Rice, who signed the treaty with Czech Foreign Minister Karel Schwarzenberg, all but ruled out going to neighbouring Poland after meeting its foreign minister on Monday.

Talks with Warsaw have run into a snag over Warsaw's demands for billions of dollars to modernise its army and air defences.

Rice said Monday's negotiations had been constructive but she would not predict whether the two sides would reach a deal.

"I believe strongly that we are at a place where these negotiations need to come to a conclusion," Rice told reporters. "We are going to have to see if we can close the remaining gap."

Under the proposed $3.5 billion (1.8 billion pound) system, an sensors and radar would be used to detect an enemy missile in flight and guide a ground-based interceptor to destroy it without using explosives.

BASES NEAR RUSSIA

Russia says the shield is a threat and has threatened to aim nuclear missiles at central Europe if it is deployed. Washington says the 10 rockets are no match for Russia's atomic arsenal.

The United States was willing to make arrangements to make the system transparent to Moscow, but Russia would also have to discuss this directly with the Czech Republic, Rice said.

Political analysts say the bases in the former Soviet bloc would raise U.S. security interests in the region at a time when Russia grows more assertive about its role on the global stage.

"Moscow, of course, sees the move as a provocation and as a long-term security threat, and will seek to extract a hefty geopolitical or strategic price for going along," said Alexandr Kliment, an analyst at political risk consultancy Eurasia Group.

Russian President Dmitry Medvedev said after meeting U.S. President George W. Bush on Monday the two sides should keep talking despite failing to overcome differences on the shield.

But Russian media quoted a Russian foreign ministry source as saying the deal complicated European security and cancelled out consultations with Moscow on the shield.

"A step has been taken . which in our view has not added to security on the European continent. More than that, it has complicated problems of security," Interfax news agency quoted a senior foreign ministry source as saying.

Rice and Schwarzenberg faced questions both about whether the system would ultimately be able to stop missiles and whether Bush's successor would follow through with the plan. Critics of the system say more tests are needed to prove it works.

"It's hard for me to believe that an American president is not going to want to have the capability to defend our territory, the territory of our allies . against that kind of missile threat," said Rice.

HURDLES

The shield still faces hurdles, including heavy opposition in the Czech Republic, a country of 10.4 million that the Soviets occupied for two decades after invading in 1968.

It also faces obstacles to ratification in the Czech parliament, where the government has just 100 seats in the 200-seat chamber. Some deputies say they will oppose it along with the Social-Democrat opposition in a vote that could come after a new U.S. administration takes over in January.

An opinion poll last month showed 68 percent of Czechs were against the shield, while only 24 percent supported it.

"We believe that this could start another arms race, and we believe this will not raise the security of the Czech Republic," said Frantisek Smrcka, who along with other protesters unfurled a huge banner shaped like a target in the Czech capital.

Rice will also travel to Bulgaria and Georgia on her European trip this week.