Shafaq News / Sweden's national security service raised its terrorist alert to the second highest level on Thursday and warned that the threat of attack could persist for a long time after burnings and other acts against the Quran outraged Muslims.

Denmark and Sweden have tightened border controls in fear of revenge attacks after anti-Islam activists damaged several copies of the Muslim holy book in recent months.

There has been widespread condemnation from many parts of the Muslim world, with Iranian Supreme Leader Ayatollah Ali Khamenei urging severe punishment for those responsible and saying Sweden was in battle mode against the Muslim world.

Sweden's SAPO security service raised the warning level from 3 to 4 on a scale from 1-5, reflecting a "high threat".

"Sweden has gone from being considered a legitimate target for terrorist attacks to being considered a prioritised target," SAPO head Charlotte von Essen told a news conference.

She said the attack threat posed by "violent Islamist actors" has increased in the past year but that the hiking of the alert level was not down to any knowledge of a specific plan.

"The increase in the terror threat level is being done to raise consciousness that the threat we see will remain for a while and society needs to build up its resistance to meet that, von Essen said.

(Reuters)