Poland and the United States on Saturday signed a deal on a future US anti-missile shield in Europe which Secretary of State Hillary Clinton said would help ward off threats from Iran.

"This is the first agreement that implements the US European-based Phased Adaptive Approach (EPAA) for ballistic missile defense and enables the stationing of a US land-based SM-3 missile defense interceptor system in the Republic of Poland," said a joint statement issued by Clinton and Poland's Foreign Minister Radoslaw Sikorski.

"This agreement marks an important step in our countries' efforts to protect our NATO allies from the threat posed by the proliferation of ballistic missiles and weapons of mass destruction," it added.

The document amends an accord signed in Washington in August 2008 after President Barack Obama modified the plan for a US anti-nuclear missile shield in Europe sealed by the previous Republican administration of George W Bush.

The original plan envisaged the installation of 10 interceptors for long-range missiles in Poland and a powerful radar in the Czech Republic. But following Russian objections that its security was threatened, the Obama government last September modified the blueprint and opted for medium- and short-range missile interceptors in Poland.

Saturday's agreement was signed in the Polish city of Krakow in the presence of Clinton and her Polish counterpart Sikorski.

The shield "will help protect the Polish people and all in Europe our allies and others from the... threats posed by Iran," said Clinton, who also exhorted Russia to get onboard.

"We believe the threats that we all face are common ones and therefore we hope that Russia will orient itself more toward working with all of us and meet those common threats," she said.

In May, Polish and US officials unveiled the first battery of US surface-to-air Patriot-type missiles to be stationed on Polish soil, a move that vexed Poland's communist-era master Russia.

In the wake of a re-evaluation of Iran's capabilities, rather than long-range missiles, the new US missile shield plan is designed to counter short- and medium-range weapons.

Sikorski said the new plan based on existing technology meant it could be implemented and work effectively. The previous missile shield project agreed by the Bush administration was based on untested missile technologies.

Clinton on Saturday refused to specify a date as to when the new defence project may be deployed on Polish soil, but defence experts have said it is likely to be ready in 2018.

On June 17 US Defense Secretary Robert Gates said that Iran was capable of launching an attack of "dozens or even hundreds" of missiles against Europe.

His Iranian counterpart Ahmad Vahidi replied the next day that Iranian missiles are aimed only at defending his country and pose no threat to other states.