Sweden increased its terrorism alert level from 3 to 4, on a scale of 5, the head of the Swedish Security Service (Säpo) announced, following angry reactions abroad over desecrations of the Koran that occurred on Swedish soil in recent months.

"Today I decided to increase the level of the terrorist threat from a high level to a critical level," said the head of Säpo, the Swedish intelligence services, Charlotte von Essen, at a press conference in Stockholm.

According to the official, the threat of attacks "will persist for a long time" in the country, since "Sweden has gone from being considered a legitimate target for terrorist attacks to being considered a priority target."

The reason for the decision is "the deteriorating situation regarding the threat of attacks against Sweden and the assessment that the threat will remain for a long time," Von Essen said, the AFP news agency reported.