MOSCOW (Reuters) - The head of an independent Russian election watchdog was detained for 12 hours at a Moscow airport Saturday as part of attempts to stop it monitoring Sunday's vote for a new parliament, the group's lawyer said. Golos leader Liliya Shibanova was held by customs officers at Sheremetyevo airport after returning from a trip abroad on the eve of the election, in which Vladimir Putin's United Russia is likely to have its huge parliamentary majority reduced. The Western-funded group's lawyer, Ramid Akhmetgaliyev, told Reuters the customs officers copied contents of her laptop computer and Golos deputy head Grigory Melkonyants said her laptop had been confiscated. Hours earlier, the United States had expressed concern about "what appears to be a pattern of harassment" of Golos, which has aired reports of alleged violations in Russian elections. A Moscow court ruled late Friday that Golos had violated a ban on the publication of opinion poll results within five days of the election to the State Duma lower house. During the campaign, Prime Minister Putin has accused foreign countries of meddling in the preparations for the election -- and for a March presidential election he is expected to win -- by funding organizations in Russia. "The pressure on Golos and its leaders (is) an attempt to block their activities involving independent public monitoring of the election," Akhmetgaliyev said. Akhmetgaliyev said customs authorities had no legal right to examine or copy the contents of Shibanova's computer and had violated her rights by preventing him seeing her during her detention. "They told me that they had information that I was supposedly bringing some sort of dangerous software across the border," Shibanova told Ekho Moskvy radio. Akhmetgaliyev also disputed the court decision, which came with a 30,000-rouble (621.68 pound) fine. He said Golos had published allegations of campaign violations, not opinion poll results. US President Barack Obama's administration expressed concern Friday about the court ruling. "The Obama administration is concerned with today's decision by a Moscow court regarding ... Golos, as well as what appears to be a pattern of harassment directed against this organization," a White House spokesman said in a statement. Before the court hearing, Moscow city prosecutors said they were investigating Golos over a complaint by lawmakers objecting to its foreign financing and urging it to stop vote monitoring. Golos, a non-profit organization founded in 2000, has a hotline for electoral violation allegations and an interactive map showing reported violations. It openly says its funding comes entirely from Europe and the United States and that this helps it remain objective. During his 2000-2008 presidency, Putin repeatedly accused the West of seeking to weaken Russia and of meddling in its affairs, including by funding non-governmental organizations meant to strengthen democracy. Formally launching his bid to return to the Kremlin next year by accepting United Russia's nomination at a party congress last Sunday, Putin reiterated these accusations last month. He said "representatives of some foreign countries are gathering those they are paying money to, so-called grant recipients, to instruct them and assign work in order to influence the election campaign themselves." He said any such activity was a "wasted effort" because Russians would reject foreign-funded politicians, comparing them to Judas, the traitor of Jesus in the bible. Critics in Russia and the West accuse Putin of curtailing democracy through a series of electoral reforms during his presidency, which coincided with an oil-fuelled economic boom. His announcement of plans to swap jobs with President Dmitry Medevedev upset some Russians who saw it as a back-room deal agreed with no regard for voters. Putin, 59, could be in power until 2024 if he wins the maximum two more terms as president. United Russia, which has dominated the Duma since 2003, is expected to retain a clear majority in the chamber though the two-thirds that allow it to pass constitutional changes without opposition support may prove out of reach. Many voters say they expect the party's result to be boosted by vote rigging and favourable coverage by traditional media. A liberal party led by former Prime Minister Mikhail Kasyanov and two allies is barred from even taking part. The biggest gainers could be the Communist Party, which is likely to remain the second biggest force 20 years after the fall of the Soviet Union. Vladimir Zhirinovsky's nationalist LDPR also hopes to gain votes from United Russia.