Swedish police have announced a search for a man accused of planning a terrorist attack in the country.

It came as the terror alert level was raised in the country from an elevated level of three, to high – just one down from the top rating in the five level scale.

The change was based on intelligence that indicated Islamic State’s intent to carry out attacks in Europe had increased.

An arrest warrant has been issued for the suspect, whose identity has not been revealed, domestic intelligence and counter-terrorism head Anders Thornberg told a press conference in Stockholm.

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“The man is being actively searched for,” Mr Thornberg said, refusing to confirm media reports the suspect was an Iraqi who had fought in Syria.

The suspect was wanted over his activities in Sweden and officials were yet to find reason he was involved in the terror attacks in Paris last week, according to Swedish intelligence service Sapo.

The change in threat level followed a reassessment, by the National Centre for Terrorist Threat Assessment, of the threat posed to the country.

“The attacks in Paris on November 13 are a possible indication of an increased capability on the part of ISIL to carry out relatively complex attacks in Europe,” Sapo said in a statement.

“Certain individuals could possibly become inspired to carry out attacks.

“Many individuals have returned to Sweden after having fought in Syria or Iraq and many are still there and could return.”

In a press conference on Wednesday (local time), Swedish officials said they had received “concrete information” that supported the need to increase the threat level.

A criminal investigation into “preparation to commit a terrorist offence” was also launched by the chief prosecutor of Sweden’s National Security Unit on Wednesday.

“We are not able to discuss this further as we are not at liberty to release any details concerning specific individuals or our operational work,” Sapo said in a statement.

NCT director Mats Sandberg told the news conference that the Islamic State group – which has claimed the Paris attacks – “considers Sweden a legitimate target”.

– with AAP