By Elise Labott
BRUSSELS (CNN) - When Secretary of State John Kerry meets Tuesday with Russian Foreign Minister Sergei Lavrov on the sidelines of NATO meetings, he will have a full agenda, starting with the crisis in Syria, disarmament talks with Iran and nuclear saber rattling by North Korea.
There also will be the issue of missile defense and ongoing negotiations between Moscow and Washington to make drastic cuts in their respective nuclear arsenals.
But the Chechen roots of the Boston Marathon bombing suspects will loom large.
While Russia could be helpful in tracing possible motivation of the alleged attackers, brothers Dzhokhar and Tamerlan Tsarnaev, as well as any possible connection to terrorist groups, the Obama administration wants to make sure it does not upset an already fragile relationship.
By CNN's Nick Paton Walsh and Catherine E. Shoichet
Something struck Tamerlan Tsarnaev's aunt when her nephew arrived in southern Russia last year.
He prayed regularly, she said. He avoided looking women in the eye. His transformation into a devout Muslim was a radical change.
By CNN Pentagon Producer Larry Shaughnessy
The number inmates participating in a hunger strike at the U.S. detention center at Guantanamo Bay, Cuba, has risen sharply in the past few weeks to include more than half of those held at the military-run facility.
Lt. Col. Todd Breasseale, a spokesman on detainee issues for the Pentagon, said on Monday the number stood at 84, up from just over 30 less than a month ago.