A growing number of radical Islamists are infiltrating Germany's military, the Bundeswehr, raising concerns of an insider attack, reports the UK Sun.

At least 80 suspected ISIS sympathizers were uncovered recently, forcing senior levels of Germany's military counterespionage service to issue a high-level probe focused on instituting background checks on all new recruits.

In the past, Germany's Ministry of Defense expressed concern that no background checks are required for soldiers in unclassified positions – a policy that enabled dozens of radical Islamists to enlist and receive military training and weaponry.

Military officials fear that a network of ISIS "sleepers" are joining the armed forces to eventually attack fellow soldiers and conduct sophisticated strikes against German society.

These reports come amid a rising ISIS threat to Germany, including deadly attacks in July and several terrorist plots foiled in the last few months.

On Thursday, German police apprehended a Syrian man suspected of planning a terrorist attack on an airport in Berlin. The man entered Germany last year as a refugee.

Several prominent examples of Islamist infiltration within the U.S. military also have caused immense concern.

A Muslim army soldier killed two comrades and injured 14 others after throwing a live grenade in a tent in Kuwait prior to the 2003 Invasion of Iraq. In 2009, U.S. Army major and psychiatrist Nidal Malik Hassan shot and killed 13 people at Fort Hood because he believed that no Muslim could faithfully serve in the U.S. military.

Three years later, Pvt. Naser Jason Abdo was arrested before he could carry out his plans to wage a second attack on Fort Hood personnel. Abdo saw it as a religious duty to retaliate for American military actions in Afghanistan and Iraq.