Magistrates in Belgium have charged a 20-year-old man with the murder of two babies and a nurse at a nursery near Brussels on Friday, prosecutors say.
The man, who prosecutors named as Kim D, was arrested hours after the knife attack in Dendermonde, in which 10 children and two adults were also hurt.
Police say he may have been planning attacks on three other nurseries, whose addresses he is reported to have had.
The suspect will appear in court on Tuesday. He has no past convictions.
Among the 12 people recovering in hospital, two young children are said to be in a very serious but not life-threatening condition.
Members of the Belgian royal family have gone to the north-western town to offer comfort to emergency workers.
Speaking at a news conference in Dendermonde, Prosecutor Christian Du Four said the man charged with the murders at the nursery was a 20-year-old from Belsele, a village about 15km (nine miles) to the north.
"We know his name - Kim D. He was interrogated for hours yesterday, late in the afternoon and during the evening. He hasn't said anything so we don't know his motives. He doesn't say anything about what happened," he said.
Mr Du Four said that when the suspect was arrested, he had been carrying a knife, a small axe and a fake pistol. He was also wearing a bullet-proof vest.
Investigators also found two knives which belonged to the man near the nursery, he added. The murder weapon was a "large knife", about 30cm (12-inch) long.
Police have denied that the man was under the influence of alcohol or drugs, or had escaped from a psychiatric institution, but correspondents say questions are being asked about why he had painted his face white, with black patches around his eyes.
Drawing a link with make-up worn by the Joker in Batman, one Belgian newspaper says the killings took place exactly one year and a day after the death of the Oscar-nominated actor Heath Ledger, who played the character in the film, the Dark Knight.
Leene Du Bois, a spokeswoman for the government of Flanders, said the suspected killer had had no connection to the nursery.
Mr Du Four said he would not comment on whether other attacks were planned, but local media have reported that police also found the addresses of three other nurseries in the man's possession.
'Multiple stab wounds'
The attack reportedly began after a man rang the doorbell at the Fabeltjesland nursery on Friday morning and told staff he needed some information.
When they opened the door, he ran in and "quickly pulled out a knife and started using it on the children", Mr Du Four said.
"He then went up to another floor and started doing the same thing again."
A nine-month old girl, a six-month old boy and a 54-year-old nurse were killed. The 10 injured children all had "multiple stab wounds on their legs, arms and all over their bodies", doctors said.
Earlier, parents had been asked to identify their children from digital photographs taken at local hospitals.
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