PARIS (AFP) - World powers threatened new sanctions against Iran on Monday after Tehran defiantly pledged to build 10 more uranium enrichment plants, but Russia warned against further escalating the dispute. Irans weekend vow to build the plants sparked strong reactions from the United States, Germany, Britain and France four of the six world powers negotiating with Tehran over its nuclear programme, as well as from the EU. But Russias energy minister said Moscow was against escalating Irans nuclear row while no immediate reaction was available from China. Backing from China and Russia, close trade partners with Iran, would be key to imposing new penalties. France was outspoken in its condemnation. Foreign Minister Bernard Kouchner branded Irans threat ridiculous and childish. German Foreign Minister Guido Westerwelle said Iran would face new sanctions if it builds the plants. What is clear is that if Iran rejects the hand that has reached out, it must expect heavier sanctions, Westerwelle said in a statement. Irans announcement that it plans to build another 10 uranium enrichment plants is unacceptable, US ambassador to the United Nations Susan Rice said Monday. We view the Iranian announcement, if it is in fact accurate and implemented that they intend to build 10 additional facilities, as completely inappropriate and further isolating Iran from the international community. We view that frankly as unacceptable, Rice said. Britain could begin mulling new sanctions next month, PM Gordon Browns spokesman said, while also stressing the importance of talks. British Foreign Secretary David Miliband said that instead of engaging with us, Iran chooses to provoke. Iran can flaunt its isolation but this will only increase the calm, determination and unity of the international community, Miliband said. EU foreign policy chief Javier Solana said he regretted Tehrans wrong decision. I lament that they have taken this decision. I still hope there will be a possibility to change their mind, Solana said. Russia and China had backed the IAEA resolution on the plant near the holy city of Qom. Western countries suspect Irans nuclear programme is aimed at building atomic weapons, a charge that Tehran has consistently denied. Russian Energy Minister Sergei Shmatko, who was visiting Iran on Monday, said Moscow wanted to see more talks. I think there is still good scope to continue negotiations, Shmatko told a joint media conference with Iranian Foreign Minister Manouchehr Mottaki.