MOSCOW (AFP) - Russia and the United States agreed on Saturday to step up cooperation in their fight against terror in the wake of news that two ethnic Chechens were suspected of organising the deadly Boston Marathon bombings.

The Kremlin said Russian leader Vladimir Putin called US President Barack Obama to once again express his condolences and discuss ways the two sides can work more closely on security in the runup to the 2014 Winter Olympic Games in Sochi.

"Both sides underscored their interest in bolstering the close cooperation of Russian and US special services in the fight against international terrorism," the Kremlin said in a statement.

"I think that contacts will be conducted between our intelligence services," Mr Putin's spokesman Dmitry Peskov said in separate televised remarks.

US authorities said that the two young men who set off twin bombs on Monday that killed three people at the Boston Marathon and then shot dead a policeman on Friday were ethnic Chechens from Russia's restless North Caucasus region.

The 26-year-old older brother Tamerlan Tsarnaev was shot and killed by police while his 19-year-old sibling Dzhokhar Tsarnaev was apprehended near Boston on Friday evening.

Analysts say that cooperation between the US and Russian intelligence services remains weak due to temperamental diplomatic ties and concern in Washington that Mr Putin was using the fight against terror to crack down on his political foes.