In their latest act of terrorism, the Islamic State was reported to have sent letters to European civilians ordering them to convert to Islam within three days or face decapitation in their own homes.

The report from Express UK said that the Daesh Islamists posted notes through the doors of random neighbors in several cities in Sweden, including its capital, Stockholm, threatening to murder "non-believers" in a violent campaign.

After receiving said threats, Sweden is now on lockdown, with intelligence officials confirming that they are investigating the notes signed by the Islamic State.

Written in Swedish, ISIS ordered people to convert to Islam or pay a religious tax called the Jizya, warning them that the police "will not save you from being murdered."

The threats stated, "In the name of Allah, the merciful, full of grace. You who are not believers will be decapitated in three days in your own house. We will bomb your rotten corpses afterwards."

It gave the people three choices that will affect their lives forever: "You must choose between these three choices: 1. Convert to Islam. 2. Pay the jizya [religious tax] for protection. 3. Or else, you will be decapitated."

As it turned out, Sweden is not the only country being threatened by the Islamic State with mass decapitation and killing. According to The Daily Mail, one of the 3,000 Assyrian Christians in Gothenburg, Markus Samuelsson, also found his own restaurant covered with the same message. He told the outlet, "I felt a sudden chill down my spine. It's terribly painful. We feel threatened."

Samuelsson is not the only victim, either. Local news outlets have reported that two Muslim asylum seekers of Irqi origin were also recipients of the same letter.

However, while the notes allowed the extremists to identify and drive out those Christians who lived in the dwellings, HNGN noted that terrorism expert Magnus Ranstorp said that Gothenburg itself has become the "Swedish Center for Jihadists," with at least 150 of its residents leaving the country to join ISIS.

Emile Anderson, police chief of Sigtuna admitted that officers at this point are not sure whether or not the threats are real, although he did say that they are taking the said cruel letters seriously.

The threatening messages only added to the tension that has already been running high in Sweden, especially considering its open door asylum policy, which has seen over 200,000 Middle Eastern migrants move to the sparsely populated area this year alone. There have already been reports of clashes between refugees and locals, and last month, the Swedish police already raided a refugee housing unit for suspicions of 22-year-old Mutar Muthanna Mahid plotting an ISIS-inspired attack.