Sweden's domestic security service, SAPO, raised its terrorism alert to the second highest level on Thursday.

It follows a series of Quran burnings and other acts against Islam's holy book in the Scandinavian country in recent months.

"The reason for this decision is the deteriorated situation with regard to attack threats to Sweden and the assessment that the threat will remain for a long time," the head of the SAPO, Charlotte von Essen, said in Stockholm.

The Swedish armed forces also said they were raising the terrorism threat level for operations.

Sweden a 'prioritized target'

Von Essen stressed the attack threat posed by "violent Islamist actors" has increased, but the alert level was not raised due to any knowledge of a specific plan.

"Sweden has gone from being considered a legitimate target for terrorist attacks to being considered a prioritized target," she said.

Sweden's domestic security service boss Charlotte von Essen urged people in Sweden to continue to live 'normally' despite the higher threat level Deutsche Welle

Islamophobic actions by small groups in Sweden and Denmark have recently sparked angry protests and threats in several Muslim-majority countries.

"We know that planned terror attacks have been averted," Swedish Prime Minister Ulf Kristersson said without providing further details.

At the weekend, al-Qaeda called for attacks against the country.

Last week, a Molotov cocktail was thrown at the Swedish Embassy in Beirut, though it did not explode.

In July, Iraq expelled Sweden's ambassador, and its embassy in Baghdad was attacked and set ablaze by angry Muslims.

On Sunday, Britain's Foreign Office warned travelers that "terrorists are very likely to try and carry out attacks in Sweden."

Sweden's problem with blasphemy

Sweden has no blasphemy laws prohibiting the burning of religious texts, and Swedish police allowed the protests, by a handful of demonstrators, citing freedom of speech.

While acknowledging the protection of freedom of speech and assembly laws under the Swedish constitution, the government has strongly denounced the desecration of the Quran.

The PET intelligence agency in neighbouring Denmark said Thursday that Quran burning had also increased the threat of attacks there, but it had no plans to raise the terror alert level.