U.S. Ambassador to Russia John Beyrle observes a minute of silence as he flowers in memory of those killed in Monday's bomb explosion at Moscow's Domodedovo airport January 26, 2011. Prime Minister Vladimir Putin vowed revenge on Tuesday for the suicide bombing that killed at least 35 people at Russia's busiest airport and underscored the Kremlin's failure to stem a rising tide of attacks. REUTERS/Sergei Karpukhin (RUSSIA - Tags: CRIME LAW TRANSPORT POLITICS)