In a rallying cry, foes brand Putin win an insult By Alissa de Carbonnel MOSCOW (Reuters) - Opponents of Vladimir Putin branded his election victory an insult to the Russian people Wednesday, trying to inject life into protests which risk fading after his return to the Kremlin. Their statement by the protest organizers signaled their determination to press on with demonstrations against the former KGB spy despite his triumph in Sunday's election and the detention of hundreds of people at rallies Monday. But the message from the League of Voters, which unites nationalists, liberals and leftists as well as independent groups, offered little new for demonstrators increasingly demoralized by their inability to change a political system dominated by Putin despite three months of protest. "Against the backdrop of widespread violations, the League finds it impossible to recognize the results of the 2012 presidential elections in Russia," the League said in a statement issued at a news conference. The elections were not fair because the vote-counting and the way the results were compiled were marked by systematic fraud which greatly distorted the result of how voters expressed their will. The Central Election Commission has said there were no major voting irregularities in the election and Putin, returning to the presidency after eight years as head of state until 2008, said he won a clean victory. Putin, who has served as prime minister for four years, has won a new six-year term and could rule as long as Soviet leader Leonid Brezhnev, whose 18 years in power have been called the "years of stagnation." Putin's spokesman, Dmitry Peskov, swiftly dismissed the opposition criticism and indicated it would not be taken into account. All assessments have been made. The matter is closed," he told Interfax news agency. Official results showed Putin won more than 63 percent of votes in the election, but independent international monitors said the poll was skewed to favor the prime minister. The United States and the European Union have called for all reports of voting irregularities to be investigated but also underlined the need to keep cooperating with Russia. The League of Voters, which was born from protests that were sparked by allegations of fraud in a parliamentary poll on December 4 won by Putin's party, said that "civil society in Russia was insulted" by Sunday's election results. "The Russian presidency as an institution, the Russian electoral system and the state authorities in Russia as a whole were discredited," it said in the statement. Police detained hundreds of people who attended unsanctioned rallies in Moscow and St Petersburg Monday and protesters who refused to leave after a Moscow rally that had been permitted. The police said they had acted in accordance with the law and Peskov defended the intervention. But some opposition leaders have said they fear Putin has decided to use force to smother their protests. The next test of their staying power will be Saturday when they plan to protest in the Russian capital, Moscow. writing by Timothy Heritage; editing by Elizabeth Piper