US President Barack Obama spoke to President Vladimir Putin on Friday and thanked him for Russia's anti-terror help after bomb attacks in Boston blamed on two men of Chechen origin.
"President Putin expressed his condolences on behalf of the Russian people for the tragic loss of life in Boston," said a White House statement.
"President Obama thanked President Putin for those sentiments, and praised the close cooperation that the United States has received from Russia on counter-terrorism, including in the wake of the Boston attack.
"The two leaders agreed to continue our cooperation on counter-terrorism and security issues going forward."
Russia has sought through two brutal wars to impose calm on the North Caucasus region of Chechnya since 1994, fighting against increasingly Islamist rebels in what Moscow has long insisted is its own "war on terror."
News of Obama's call with Putin came as new shots rang out over the Boston suburb of Watertown, amid reports that police had surrounded teenaged Boston marathon bombing suspect Dzhokhar Tsarnaev.
Tsarnaev's older brother Tamerlan was killed in a shootout with police earlier Friday.
Both men, who were in the United States legally, were suspected of carrying out the bombings on the Boston marathon on Monday that killed three people and injured around 180 others.