Poland and the United States on Wednesday signed a deal to set up a missile defence base on Polish soil, part of a planned US system in eastern Europe that has inflamed tension with Russia.

After more than a year of tough bargaining, Poland formally agreed to host 10 US missile interceptors in return for a pledge of American military aid, including a battery of Patriot air defence missiles.

"It is really not just a historic occasion, but an extraordinary one," US Secretary of State Condoleezza Rice said after she and Polish Foreign Minister Radoslaw Sikorski signed the deal in Warsaw.

"Our countries, Poland and the United States, will be more secure," said Polish Prime Minister Donald Tusk.

The Czech Republic is to host the other part of the system, a tracking radar near the German border. If parliaments in both nations agree, the two former Soviet-bloc nations will get their first US bases.

Last week's news that Polish and US negotiators had an accord led to speculation that Russia's invasion of Georgia spurred Poland to close the deal.

Russia has fiercely opposed the planned shield, despite repeated US assurances that it would defend Europe and the United States against missile threats from "rogue nations" like Iran, not target Moscow's strategic nuclear arsenal.

Poland bargained hard for US military aid, particularly for a boost in its air defences after Moscow threatened to target the planned missile-shield bases in its former satellites.

The interceptors are designed to destroy incoming intercontinental ballistic missiles in space. In contrast, the Patriots sought by Poland are theatre defence weapons with a range of about 70 kilometres.

Earlier, Rice insisted that the missile shield posed no threat to Russia.

"We're talking about a missile defense system that couldn't possibly be aimed at the Russian nuclear deterrent," she told the BBC on Tuesday. "Russia has thousands of nuclear warheads. This is for small missile attacks of the kind that Iran might launch."

The Pentagon expects the missile shield to be in full operation by 2013. To blunt Russian fears, the US offered Russia to join the project or inspect the planned sites.

Sikorski last week renewed "our offer" for Russian inspections. He also reached out to Moscow, while denouncing its "brutal" assault in Georgia.

"When the smoke has cleared after the battle, we will stay neighbours," he wrote in the Polish daily Fakt.

While the US plan has been unpopular among Czechs and Poles, latest polls in Poland show that opinion had swung in favor of the shield in the wake of the fighting over South Ossetia between Russia and Georgia.

Many Poles view Russia's military incursion into Georgia as proof that Poland needs a strong defence.

In a sign that Poland's government - although more EU-friendly than the previous one - wants stronger ties with the US, the agreement included a pledge of US military cooperation sought by the Poles.

The document says the US is "committed to the security of Poland and any US facilities on the territory of Poland," Tusk told the signing ceremony.

The Bush administration began sounding out Poland and the Czech Republic about four years ago. Formal talks with Poland began in May 2007, but they hit a snag after Tusk came to power in November and sought an improved deal for Poland.

Polish President Lech Kaczynski called the signing an "important day" in Polish history during a televised address to the nation Tuesday.

Poland had taken a step to "strengthen its position in the world" by sealing the agreement with Washington, he said.