MOSCOW (CNN) — International observers blasted Russia’s presidential election Monday, saying: “The point of an election is that the outcome should be uncertain. This was not the case in Russia.”

Russian Prime Minister Vladimir Putin looked set to win Sunday’s vote and return to the office he held until he was forced out by term limits four years ago.

But European monitors expressed disappointment and frustration with the way he won.

They said they observed ballot stuffing and other irregularities in about a third of polling stations they monitored, and an uneven playing field in the run-up to the election.

Sounding somewhat exasperated, the Council of Europe’s Tiny Kox urged Russia “to have a fair election,” saying “it’s not that difficult.”

Ambassador Heidi Tagliavini of the Organization for Security and Cooperation in Europe was particularly critical of irregularities in vote counting because “what matters in an election is the counting,” she said.

She declined to say whether the irregularities affected the outcome of the vote — a landslide for Putin by international standards, if not Russian ones.

And she praised incremental improvements such as web cameras in polling stations and transparent ballot boxes, as well as the “massive mobilization of civil society demanding fair elections.”

French Foreign Minister Alain Juppe said France will continue its partnership with Russia but said the OSCE’s criticisms are important.

“The election has not been exemplary, to say the least,” Juppe said.

Putin called for unity Sunday night as he appeared headed for a third term as president, declaring he had won an “open and honest fight.”

But chess champion-turned opposition activist Garry Kasparov accused Putin’s supporters of “massive fraud,” saying early Monday they packed the polls with additional voters.

With better than two-thirds of the vote reporting early Monday, Putin led his closest rival by a nearly 4-to-1 ratio. His margin of victory was smaller than in 2004, the last time he ran for president, but appears well above the 50% needed to avoid a runoff.

“We have won an open and honest fight,” Putin told the cheering and flag-waving supporters who had braved the cold in Manezhnaya Square for hours to hear his expected victory speech. The results show “that our people are ready for renewal, and have only one aim.”

“We are appealing to all people to unite for our people, for our motherland, and we will win,” he said. “We’ve had a victory! Glory to Russia!”

The 59-year-old former KGB officer served two terms in the Kremlin before term limits forced him to step down in 2008. But he served as prime minister under his successor, Dmitry Medvedev, and continued to dominate Russian politics.

With more than 68% of boxes reporting, Putin had just under 65% of the vote in a field of five candidates. His closest challenger, Communist leader Gennady Zyuganov, had slightly more than 17%; the other three candidates — including billionaire Mikhail Prokhorov, the owner of the New Jersey Nets basketball team — were running in the single digits.

Presidents Hugo Chavez of Venezuela and Bashar al-Assad of Syria on Monday congratulated Putin on his win, but opposition figures said they planned to continue their demonstrations, fueled by new complaints about Sunday’s results.

Roughly 50 supporters of the banned National Bolshevik Party were detained Monday in Moscow for attempting to hold an unauthorized rally, Russia’s Ministry of Internal Affairs said.

Kasparov, who served as a poll watcher in his Moscow neighborhood, said Putin’s supporters “simply added new voters to the register using so-called supplementary voter rolls.”

“At one of the polling stations, the number of extra voters even exceeded the number of registered voters,” he said.

And Ilya Ponomarev, a member of parliament and a prominent protest figure, said he did not feel there was a fair counting of votes. Many polls before the vote, he said, showed Putin receiving around 40%.

“Mr. Putin remains to be one of the most popular politicians in the country, probably the most popular politician in the country, and it’s quite natural that he’s receiving the majority of the votes,” Ponomarev, of the A Just Russia party, told CNN from Moscow’s Red Square. “But it should not be an overwhelming majority, and I think there has to be a runoff.”