The U.S. issued a travel warning for Americans traveling to Sweden and Turkey this week, urging them to avoid crowded places and use caution when using public transportation and attending religious events.

The U.S. embassy issued the travel warning after the Swedish government received word from Iraq that ISIS members may be planning to attack civilians in the capital of Stockholm.

“The U.S. Embassy in Stockholm has confirmed that Swedish Police are actively investigating a potential terror threat against Sweden.”

A travel alert for Turkey was also issued late Tuesday night by U.S. officials who say they have information about credible threats leveled against high profile tourist areas.

US expats told to 'avoid crowds' as Swedish police continue to probe potential terror threat https://t.co/THnUFbKkyT pic.twitter.com/oDTc3Rr17z — The Local Sweden (@TheLocalSweden) April 27, 2016

Seven or eight Iraqi citizens who were formerly al-Qaeda members are thought to have snuck into Sweden along with the human wave of Syrian refugees flooding the continent.

Nearly 163,000 people applied for asylum in Sweden last year with 21,000 of those coming from Iraq, and the refugee crisis could easily have allowed terrorists to slip into the country, counterterrorism expert Magnus Ranstorp, told NBC News.

“There were so many refugees who came in at once, many on false identities, so many were not checked or registered properly. It would be easy for them to hide and move around quite freely, also difficult for the police to trace them.”

Some 3,000 to 5,000 Europeans have returned to the continent after receiving terror training from ISIS in Iraq and Syria, while at least 300 Swedish citizens have left the country to join the terror group in the Middle East, according to RT News.

“Terrorist groups continue to plan near-term attacks throughout Europe, targeting sporting events, tourist sites, restaurants, and transportation.”

Security Message for US Citizens: Police Investigation of Possible Threat in Sweden: https://t.co/nO5dKRvmZs pic.twitter.com/w2QHZ8IY0z — US Embassy in Sweden (@usembassysweden) April 27, 2016

The European continent has been struck by massive terror attacks twice in recent months. In November 2015, three suicide bombers struck Paris and a nearby suburb killing 130 and injuring another 368. Then, in March, terrorists struck again in Brussels killing 32 people and injuring another 300.

After the Brussels terror attack, fears of another strike spread through the European continent, and security officials admitted to knowing of terrorists who infiltrated the country using the human flood of refugees as cover.

US Intelligence Chief: Open Borders Has Allowed ISIS to Set Up Sleeper Cells in UK, Germany https://t.co/KZDPZIX9Lw pic.twitter.com/DUquHc0UeZ — Breitbart London (@BreitbartLondon) April 27, 2016

Now, with those terrorists in place and the security warning already issued, it’s entirely possible the militants are preparing to attack the Swedish civilian population in a dramatic fashion.

In a sick and twisted poll, ISIS leaders asked their followers to choose the next terror target days after the Brussels attack; Sweden wasn’t on the list of 10 countries.

Festivities to honor Swedish King Carl XVI Gustaf are heightening security concerns as some worry ISIS will attempt to take advantage of the situation to sow confusion and fear. Sweden’s national terror threat level remains unchanged, however, at level three on a five-point scale; security at national airports also remains low.

US Embassy Islamabad continues to receive reports of possible terrorist attacks against various locations https://t.co/xCs9nxn5P3 — Travel - State Dept (@TravelGov) April 27, 2016

Sweden’s security police, Säpo, met with Eurovision organizers Tuesday to discuss security measures for the Eurovision Song Contest scheduled for May, a press officer told The Local.

“Säpo is working intensively on assessing the information received. It is of such a nature that we cannot dismiss it. We are currently collecting information and intelligence.”

The last Swedish terror attack was in 2010 when a suicide bomber detonated two bombs along a busy Stockholm street injuring two innocents.

The U.S. also issued travel warnings for Americans traveling in Turkey late Tuesday with American security officials continuing to receive reports that ISIS is planning to strike popular tourist destinations in the country.

[Photo by Vittorio Zunino Celotto/Getty Images]