The United States and the Czech Republic signed an initial agreement Tuesday to begin basing part of a U.S. intercontinental ballistic missile shield in the former communist country.

Secretary of State Condoleezza Rice said the shield is a good deal for the Czech Republic and for Poland, where the United States hopes to place another part of the system, although Warsaw hasn't yet agreed.

The next U.S. president will have to decide whether and how to go forward with the missile defence system, Rice said, while making the case that the threat from Iran is growing and it is hard to imagine any administration giving up an effective deterrent.

"It's hard for me to believe that that's not a capability an American president is going to want to have," Rice said.

Rice signed the agreement with Czech Foreign Minister Karel Schwarzenberg.

Rice had all but ruled out a stop in Poland this week to finalize plans for a U.S. missile defence shield in Europe, saying Tuesday that the United States has answered Polish demands for military hardware and the final agreement rests with Polish authorities.

Officials said she had hoped to make the week's visit in Eastern Europe a clean sweep for the unproven anti-missile defence system, which is bitterly opposed by Russia as an affront to its sovereignty and a potential threat should the system one day be used against Moscow.

Poland's continuing demands are seen by the U.S. as an obstacle to begin building the missile shield before President George W. Bush leaves office early next year.

"We are at a place where these negotiations need to come to a conclusion," Rice told reporters.

Scheme unpopular in Europe

The missile systems, which the United States says are defences against long-range weapons from the Middle East, especially Iran, are highly unpopular in both the Czech Republic and in Poland — both former satellite states of the old Soviet Union.

As part of the plan, the U.S. wants to place its own missiles and interceptor aircraft on Czech and Polish soil in the next five years.

"Ballistic missile proliferation is not an imaginary threat," Rice said after meeting Czech Prime Minister Mirek Topolanek. She said Iran continues to perfect the tools it might one day use to build a bomb, along with long-range missiles that could carry a warhead.

Moscow has threatened to aim its own missiles at any eventual base in Poland or the Czech Republic.

In 2005, Canada formally declined to take part in the U.S. missile defence scheme, citing national sovereignty concerns, but Prime Minister Stephen Harper’s Conservative government is thought to favour the plan while accepting that it would never be approved by the current Parliament.

With files from the Associated Press