Merkel said she had been stunned by the massacre in the southwestern town of Winnenden, near Stuttgart, where 17-year-old Tim Kretschmer shot 15 people with his father's pistol, including 12 at his former school, before killing himself.

"The lesson is that we must be attentive to all young people -- that's true for parents and educators," Merkel told Deutschlandfunk radio.

"We must do all to prevent children from having access to weapons and from them having to face too much violence."

The tragedy in Winnenden has sparked calls by some politicians to tighten German weapon laws. But Interior Minister Wolfgang Schaeuble, a member of Merkel's Christian Democrats, ruled that out in a Reuters interview last week.

Merkel said it was crucial that rules on the storage of weapons and munitions were applied.

"Experts will certainly consider: Would it be possible to ensure (the compliance to rules) even further through unannounced controls or other means?" she said, without explaining whether she referred to checks at private homes.

Kretschmer shot many of his victims in the head with his father's legally registered Beretta.

His father, a member of a shooting club, had 15 guns at home. Fourteen of those were locked in a gun closet as required by law but the Beretta was in the bedroom, officials said.

Germany toughened gun laws in 2002 after a 19-year-old shot dead 16 people and himself at a high school in east Germany.

Merkel said she was also considering what could be done to limit access to violent video games, but did not give details.

German media said Kretschmer, who neighbours described as a loner, had played a violent game on his computer a few hours before he went on his shooting rampage.