Moscow ? A double suicide bombing that killed 15 people at a Moscow rock festival had a chilling effect on the Russian capital Sunday with mourners at a memorial service worrying about safety in the city and President Vladimir Putin postponing a trip.

As flowers piled high at a makeshift memorial at the scene of the blasts, Putin put off traveling to Uzbekistan and Malaysia in a trip that was to start Sunday.

The Kremlin gave no explanation for the delay, although it reflects Putin’s sensitivity to accusations he is aloof in times of crisis.

“The goal of this terrorist act is obvious — to seed fear, suspicion and ethnic intolerance in our society,” Putin said in a statement released Sunday to Russian news agencies. “We know that betrayers of their own people and murderers don’t have and can’t have a future.”

Two people died overnight of injuries from the attack, bringing the death toll to 15, including the two female bombers, said Lyubov Zhomova, a spokeswoman for the Moscow Health Directorate.

The Interior Ministry responded to the attacks by stepping up security in Moscow — where memories are still fresh of the hostage-taking raid on a theater last October that ended in the deaths of 129 hostages and 41 Chechen captors.

Student Dmitry Grachyov returned Sunday to the site where he was injured in the arm and leg by ball bearings packed inside the explosives. He laid a bouquet of flowers on a wall near the entrance to the Tushino airfield where the festival took place.

Grachyov, 17, said he was skeptical that increased security could have prevented the attacks. “The security measures were tough, but you never know when and where a disaster can happen. No matter how careful you are, anything can happen anywhere,” he said. “I survived the shock. Now I am scared that it could have been worse.”