Sweden heightened its terrorism alert level to the second highest after a series of incessant desecrations of the Quran, as Prime Minister Ulf Kristersson said the country recently foiled planned terrorist attacks.

Sweden has in recent weeks asked citizens abroad and businesses linked to the country to "be attentive and aware of the information the authorities communicate," following a string of public burnings of copies of Islam's holy book.

"We know that planned terrorist acts have been prevented," Kristersson told a news conference on Thursday. "These are people who have simply been arrested. Both in Sweden and abroad." He did not elaborate.

The Scandinavian country's domestic security service, SAPO, said the overall security situation has deteriorated and the risk of terrorism in Sweden was now at level four - a "high threat" - on its five-point scale, a first since 2016.

"We are in a deteriorating situation and this threat will continue for a long time," SAPO head Charlotte von Essen said at a separate news conference.

She said that Sweden is currently regarded as "a priority target" for such attacks.

While urging people in Sweden to continue to live "normally," von Essen stressed that there wasn't a single incident that led to the heightened threat level.

"I understand that many Swedes are concerned about the meaning of the new and higher threat level," Kristersson said. "We stand up for our democratic values, but we protect ourselves."

"Swedish police are ready to face this situation," the country's national police chief Anders Thornberg said.

Kristersson reiterated Thursday that Swedes abroad and Swedish interests also should be vigilant and cited the storming of Sweden's Embassy in Baghdad last month and an attempted attack on the diplomatic mission in Beirut last week.

Denmark's national police said Wednesday that "on the recommendation" of the domestic intelligence service PET, it was "necessary to maintain the temporarily-intensified efforts at the internal Danish borders." Sweden has also stepped up border controls and identity checks at crossing points.

On Tuesday, PET and its foreign intelligence counterpart said in a joint statement that the recent Quran burnings "have resulted in considerable, negative attention" from terrorists. The terror alert level in Denmark is also at the second-highest level.

The recent burnings of the Quran have further complicated Sweden's attempt to join NATO, a step that has gained urgency after Russia's invasion of Ukraine last year. In July, President Recep Tayyip Erdoğan signaled that the burning incidents would pose another obstacle to Sweden's bid. To join NATO, Sweden needs the approval of all of its current members, including Türkiye, which has been in the alliance for over 70 years and boasts its second-largest army.

Like many Western countries, Sweden doesn't have any blasphemy laws that prohibit the burning of religious texts and Swedish police allowed the protests, by a handful of demonstrators, citing freedom of speech.

Erdoğan strongly condemned the desecration of the Quran in Sweden, saying that the hostile act cannot be evaluated under freedom of expression.

The U.N. human rights chief Volker Türk during a debate last month called for respect of "all others," including migrants and women and girls who wear headscarves while affirming the right to freedom of expression.

The Quran desecration incidents "have contributed to the image of Sweden as a country hostile to Muslims," the head of the National Centre for Terrorist Threat Assessment, Ahn-Za Hagstrom, told reporters at the same news conference.

Iraqi protesters stormed the Swedish embassy in Baghdad twice in July, starting fires within the compound on the second occasion.

The Jeddah-based Organisation of Islamic Cooperation (OIC) has also voiced "disappointment" with Sweden and Denmark for not taking action following the burnings.

Kristersson said Sweden was engaged in intense diplomatic efforts with Muslim countries in a bid to calm the "difficult" situation.

Travel warnings

Several Western countries had recently updated their travel advisories for Sweden, even before it raised its threat assessment.

On July 26, the United States urged its nationals to "exercise increased caution in Sweden due to terrorism."

And on Sunday, Britain's Foreign Office said: "Terrorists are very likely to try and carry out attacks in Sweden."

Sapo said meanwhile it had indications foreign actors were fuelling the negative narrative about Sweden.

"We know that extremist groups and foreign powers gladly use these kinds of situations that Sweden now finds itself in... They exploit this to sow further divisions," said Sapo's deputy head of counterterrorism Susanna Trehorning.