The 2014 Winter Olympics host Russia on Tuesday vowed to step up security measures at sporting events after deadly Boston marathon blasts that it described as a "big warning".
Security has been a top concern for Russia as it prepares for marquee events such as the 2014 Winter Olympic Games in Sochi and the 2018 Football World Cup.
It is already hosting massive events this summer with the World Athletics Championships in Moscow and the Universiade world student games in the Volga city of Kazan.
Russian Sports Minister Vitaly Mutko said the Boston marathon attack underscored the need for the utmost vigilance at fixtures that attract global interest and major television audiences.
"For Russia, which will soon have to stage a number of big sporting events, this is a serious warning bell," the RIA Novosti news agency quoted Mutko as saying. "Of course we are tightening up security measures."
He added that Russia's security plan was "already very serious" and officials would redouble their efforts on "avoiding these situations".
The Sochi Games will be staged on the edge of the volatile Caucasus region where Russia waged two post-Soviet wars in Chechnya and which now suffers from weekly violence in nearby Dagestan.
Officials in 2011 claimed to have uncovered a complex terror plot against the Games by Islamist rebels who allegedly used little-policed mountain regions of Georgia as their base.
Mutko admitted that Russia was "very worried" about security at all its sporting events.
"We will be devoting special attention to it," he said.
The Kremlin said separately that Russian leader Vladimir Putin had sent US President Barack Obama a message of condolences in which he condemned "this barbaric crime".
Putin said "the fight against terrorism" requires the coordinated international efforts and that Russia was ready to help in the Boston investigation.
The athletics event in August will bring world stars to Moscow such as the Jamaican sprinting world record holder Usain Bolt.
The Kremlin views the championship as a test-run for Sochi preparations, and officials promised a level of security rarely seen at sporting events.
"Moscow will see a triple level of security" composed of state agents as well as Moscow police and stadium personnel, Russian Federal Athletics Federation chief Valentin Balakhnichev told RIA Novosti.
"This tragedy showed that we are poorly protected against evil intentions. The most important part of our sport is the audience. We have to protect them the best we can during the event," Balakhnichev said.
An unnamed Russian federal security source also told the Interfax news agency that the Boston attack "cannot be left without our attention".
And the sports ministry in the Tatarstan region where the Universiade will be held in July also vowed to set up security in response to the Boston blasts.
"No one is insured against the threat of extremism and terror," the regional sports ministry said in a statement released on its website.
"This is why the issue of providing security is our number one job."
The twin explosions 13 seconds apart in Boston killed at least three people and wounded more than 100 as runners participating in the 26.2 mile (42-kilometre) race approached the finish line.
The Sochi Games Organising Committee chief Dmitry Chernyshenko said in a statement that he was "deeply saddened by the news coming from Boston" and expressed his condolences to the victims' families.