Russian Prime Minister Vladimir Putin led growing support Thursday from some world leaders for the beleaguered WikiLeaks founder, describing his detention in Britain as 'undemocratic'. The wave of support for Julian Assange, who sat in a British jail Friday as Sweden sought his extradition on rape charges, came as hackers -- dubbed 'hack- tivists' -- stepped up cyber attacks on those opposed to WikiLeaks. After taking down the websites of Visa, Mastercard and others, supporters of the whistleblower website tried but failed to knock online retail giant Amazon.com offline. The loose-knit group of hackers known as 'Anonymous' said they would attack the Amazon website as part of what they are calling 'Operation Payback'. The Amazon.com website did not appear to have experienced any downtime, and Anonymous acknowledged defeat on another Twitter feed -- then instructed supporters to switch their cyber attacks to the website of Internet payments company PayPal. Dutch police, meanwhile, said Thursday they arrested a 16-year-old who has admitted to staging cyber attacks on on Visa and Mastercard sites in support of WikiLeaks. The teen, who was 'probably part of a larger group of hackers,' will appear before a judge on Friday, said Wim de Bruin, spokesman for the national prosecutor's office. Putin railed against the detention of the 39-year-old Assange, the Australian founder of the website which has been releasing thousands of secret US diplomatic cables as well as Pentagon communiques. 'Why was Mr. Assange hidden in jail? Is that democracy? As we say in the village: the pot is calling the kettle black,' Putin said. 'I want to send the ball back to our American colleagues,' Putin added. Despite his defence of Assange, Putin was portrayed in an embarrassing light by some of the leaked cables. In one, US Secretary of State Hillary Clinton called him a 'behind the scenes puppeteer' dissatisfied with his role. Others detailed allegations of high-level Russian corruption and referred to Putin as an 'alpha dog'. His comments echoed Brazil's President Luiz Inacio Lula da Silva, who expressed 'solidarity' with Assange, blasting the Australian activist's arrest as a blow against 'freedom of expression'. Assange has 'exposed a diplomacy that had appeared unreachable,' said Lula. 'They have arrested him and I don't hear so much as a single protest for freedom of expression,' he said. Meanwhile, Navi Pillay, the UN High Commissioner for Human Rights, hit out at pressure being exerted on 'private companies, banks and credit card companies' to cut commercial ties to WikiLeaks. 'They could be interpreted as an attempt to censor the publication of information, thus potentially violating WikiLeaks' right to freedom of expression,' she told a press conference in Geneva. Anonymous told selfnews in an online chat they would attack anyone they perceive as having an 'anti-WikiLeaks agenda'. The Swedish government's website was forced offline as was the office of the Swedish prosecutor. WikiLeaks distanced itself from the group in a statement, saying it had no affiliation with Anonymous. 'There has been no contact between any WikiLeaks staffer and anyone at Anonymous. WikiLeaks has not received any prior notice of any of Anonymous' actions,' the website said in a statement. WikiLeaks spokesman Kristinn Hrafnsson said in the statement: 'We neither condemn nor applaud these attacks. We believe they are a reflection of public opinion on the actions of the targets'. Assange's supporters have vowed the arrest will not halt the flow of secrets, with the latest revelations causing more embarrassment for Washington. One leaked cable out Thursday says that dockworkers and foreign businessmen in Myanmar have seen evidence of alleged secret nuclear and missiles weapons sites being built deep in the jungle. 'The North Koreans, aided by Burmese workers, are constructing a concrete- reinforced underground facility that is '500ft from the top of the cave to the top of the hill above',' according to the cable, published by the British daily The Guardian. And a leaked cable on Thursday said Serbia in 2008 knew the whereabouts of top fugitive genocide suspect Bosnian Serb general Ratko Mladic. According to the cables released by WikiLeaks and published by The New York Times, a Spanish diplomat in the Balkans, Ramon Abaroa, claimed in 2008 that Serbia 'knows perfectly well where Mladic is.' 