Moscow braced for post-election rallies after Prime Minister Vladimir Putin was elected president in an election the opposition charged was flawed. Two gatherings by Putin supporters were scheduled for Monday, a rally at Manezhnaya Square expected to draw 20,000 people, and a concert at Revolution Square, RIA Novosti reported. With 99.5 percent of ballots counted, Russia\'s presidential elections Sunday saw Putin claim a landslide victory, capturing 63.71 percent, RIA Novosti said. Communist leader Gennady Zyuganov received 17.19 percent while billionaire-turned-politician Mikhail Prokhorov got 7.88 percent . The opposition will conduct sanctioned rallies at Pushkinskaya Square and Lubyanka Square to protest the results that opposition leaders allege were skewed toward Putin. Other opposition groups used online social networks to organize unsanctioned rallies throughout Moscow, RIA Novosti said. \"This is not an election; it\'s a shame,\" Sergei Udaltsov, the leader of the Left Front, a radical socialist group, posted on Twitter. \"Once again they spat in our face.\" Putin said Monday he plans to tell the Central Election Commission to investigate possible voting violations, RIA Novosti said. During a meeting with several election rivals, Putin said he would \"have a conversation\" with elections chief Vladimir Churov and \"will ask him to thoroughly look into all possible violations ... .\" An international monitoring agency reported Monday it found state resources were used at the regional level to support Putin\'s candidacy. Also, overly restrictive candidate registration requirements limited genuine competition. The Organization for Security and Cooperation in Europe, based in Austria, said in a statement voting generally was positive. However, monitors said nearly a third of polling stations had procedural irregularities. \"This election showed a clear winner with an absolute majority, avoiding a second round. However, [a] voter\'s choice was limited, electoral competition lacked fairness and an impartial referee was missing,\" said Tony Kox, head of the delegation to the Council of Europe\'s Parliamentary Assembly. \"Due to increased citizen\'s awareness and involvement elections were more lively, better managed and more seriously observed, whereas structural improvements in electoral regulation were proposed to Parliament -- but not yet passed.\" Presidential candidates could not \"compete on an equal footing\" and despite efforts to improve transparency, \"there remained widespread mistrust in the integrity of the election process,\" said Ambassador Heidi Tagliavini, leader of the organization\'s election observation mission. \"As a first step, all allegations of electoral violations need to be thoroughly investigated.\" Tonino Picula, special coordinator of the mission and head of the delegation of the OSCE Parliamentary Assembly, said there were serious problems from the start. \"There was no real competition and abuse of government resources ensured that the ultimate winner of the election was never in doubt,\" Picula said. The independent election watchdog Golos, a US-funded non-governmental organization, said Putin won more than 50 percent of the vote. It reported fraud allegations, including \"carousel voting,\" in which the same people cast ballots at multiple locations, and \"centralized voting,\" in which managers of factories, schools, hospitals and other large organizations pressure employees to vote for a specific candidate. In some cases, ballots are collected at the workplace. Putin previously served two terms as president, from 2000 to 2008.