Their preliminary findings said campaigning had been “clearly skewed” towards one candidate - without naming Mr Putin – with limitations on the selection of candidates and evidence of strong bias in the largely state-controlled media.
Tiny Kox, a Dutch politician and head of the Council of Europe, said at a press conference: "The competition lacked fairness and an impartial referee was missing."
Russian activists said they had tracked 4,000 examples of malpractice across the vast country's 91,000 polling stations. Mr Putin secured almost 64 per cent of the vote, winning back the Russian presidency which he held for two terms from 2000-2008 before his four-year stint as prime minister. His nearest rival, the Communist Party boss Gennady Zyuganov, trailed well behind.
The Foreign Office said it was withholding any reaction until it had read the findings of the OSCE’s election arm, the Office for Democratic Institutions and Human Rights.
"We await the preliminary report of the OSCE / ODIHR election observation mission with interest," said a Foreign Office spokesman.
"We fully support the importance of democratic elections in Russia, as elsewhere in the world. As a Council of Europe member state, Russia has an obligation to uphold key democratic norms and standards."
France gave a cool reaction to Mr Putin's return to the Russian presidency, but accepted that his controversial election victory was not in doubt.
"I take note that President Putin is our interlocutor for years to come," Foreign Minister Alain Juppe told a news conference. "Overall, despite some criticism ... the re-election of President Putin is not in doubt."
Angela Merkel, the German chancellor, however spoke to Mr Putin to wish him success in his presidency.
Relations between Britain and Russia soured over the murder of ex-agent turned Kremlin critic Alexander Litvinenko in London in 2006. He died after drinking tea laced with polonium.
Moscow has since snubbed a British extradition request for former agent Andrei Lugovoi, and the two countries have recently clashed in the United Nations Security Council over a resolution condemning the Syrian regime’s crackdown on protestors. Russia, followed by China, blocked the resolution.