White House contender Mitt Romney wrapped up a gaffe-prone tour in Poland Tuesday with a swipe about the state of freedom in Russia – and a fresh blunder by an aide who told journalists to "kiss my ass."

On his first visit behind the old Iron Curtain, the Republican nominee vowed his commitment to close ties with Poland, which still has a testy relationship with Moscow more than two decades after the fall of communism.

Hailing his hosts as "an example and defender of freedom", Mr. Romney said: "In Russia, once-promising advances toward a free and open society have faltered."

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Earlier this month, Mr. Romney criticized President Barack Obama's administration for its "abandonment of friends" in a region still wary of Russia – a country he once described as America's "number one geopolitical foe".

Poland, a country of 38 million which made a peaceful, if difficult, transition from communism in 1989, is now an economically flourishing pillar of the EU and NATO and has supplied troops for the US-led wars in Iraq and Afghanistan.

"Poland has no greater friend and ally than the people of the United States," said Mr. Romney. "I believe it is critical to stand by those who have stood by America... and it is with solidarity that America and Poland face the future."

But the final leg of the three-stop tour, aimed at burnishing Mr. Romney's foreign policy credentials ahead of the November presidential election, was marred by a verbal attack on journalists by one of his top aides.

His spokesman Rick Gorka lost his cool when journalists pressed Mr. Romney during a solemn visit to a World War II memorial in Warsaw over the gaffes that have plagued him during his visits to Israel and Britain.

Mr. Gorka told the journalists to "kiss my ass" and to "shove it" as they chased Mr. Romney for answers, before calling them half an hour later to apologise.

In Britain, Mr. Romney – who organised the 2002 Winter Olympics in Salt Lake City – triggered outrage after he questioned London's security readiness for the Games which opened on Friday.

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And in staunch ally Israel, he angered the Palestinians for endorsing Jerusalem as the capital of the Jewish state and saying that Israeli "culture" helps them succeed economically.

In Gdansk on Monday, Mr. Romney had won praise from Nobel peace laureate Lech Walesa, whose Solidarity trade union led the struggle against communist rule in the 1980s.

But Solidarity distanced itself from Mr. Romney's visit, saying it was "in no way involved" in inviting him to Poland.

"Regrettably we learned from our American friends at AFL-CIO headquarters who represent over 12 million workers about Mitt Romney's backing of attacks on trade unions and worker's rights," it said.

Poles nevertheless have long displayed an affinity for Mr. Romney's Republican party thanks to late US "Cold Warrior" president Ronald Reagan's staunch support for Solidarity and his uncompromising approach to Moscow.

"In a turbulent world, Poland stands as an example and defender of freedom," Mr. Romney said Tuesday, pointing to Belarus, Syria and the Arab world as well as Venezuela and Russia as countries still struggling for liberty.

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Earlier this month he voiced doubt over the legitimacy of the March election which returned President Vladimir Putin to the Kremlin and accusing Russia of arming the Damascus regime.

Mr. Obama's administration has been criticised in Poland for revamping an anti-missile shield project planned for the region against rogue states by its Republican predecessor but had raised hackles in Russia.

A staunch free marketeer, Romney hailed EU member Poland's reform-oriented economy, which has flourished since the demise of communism while others in Europe are mired in debt.

"The world should pay close attention to the transformation of Poland's economy," said Mr. Romney, who met Poland's top political leaders during his trip.

"A march toward economic liberty and smaller government has meant a march toward higher living standards, a strong military that defends liberty at home and abroad, and an important and growing role on the international stage."