US special forces provide military training to Iraqi security forces.

On May 4, Pentagon officials confirmed that a US Navy SEAL was killed in a `complex coordinated attack` by about 100 self-proclaimed Islamic State (IS) rebels.

A US defense official said that in this attack, IS applied a deep penetration tactic that put elite US forces in a surprised position.

Lt. Col. Manav Dosky of the Iraqi Kurdish intelligence force said at least three Kurdish militiamen were killed when their checkpoint was overrun by IS Humvees.

In the town of Telskof, 3-5 km from that line, a SEAL team has just visited and will be present here for a short time to act as military advisors to the Peshmerga.

An anonymous US defense official said this SEAL was hit by infantry rifle bullets, proving that IS rebels were only a few dozen to a few hundred meters close to the position of the US advisory group.

American press said the soldier killed in this battle was Charlie Keating IV, 31 years old, from Arizona.

The US military retaliated by sending F-15 fighter jets and drones, dropping more than 20 bombs on IS targets, a US official said.

Deep penetration with suicide bombers and modified armored vehicles is a favorite tactic of IS rebels and has caused terror to the Iraqi army and Peshmerga.

ISIS’s improved Humvee armored vehicles have always been a terror to the Iraqi army.

IS often uses suicide car bombs to destroy obstacles and blow up enemy bridgeheads, then uses infantry to attack surrounding targets.

Keating is the third American soldier to die while participating in the war against IS rebels in Iraq since 2014.

The challenge is getting bigger and bigger

The attack that led to the death of Special Agent Keating took place in the context that the US was strengthening its role in the fight against IS, when the Iraqi army was increasingly showing weakness both politically and militarily.

For nearly two years, the Pentagon has continuously poured money, equipment and special forces into Iraq to help the Kurdish army and militia in this country be capable of fighting against IS on the ground.

US Secretary of Defense Ash Carter said that by sending more US special forces to Iraq as advisors, the country’s military’s chance of success in the fight against IS is even higher.

American military advisors are facing greater challenges than ever on the battlefield in Iraq.

Last month, the Iraqi army gathered forces and announced a campaign to surround and attack IS’s Mosul base in the country.

On Monday, Defense Secretary Carter said that the Pentagon would continue to support the Iraqi military by deploying more military advisers to brigades and battalions on the front lines against IS.

US soldiers provide artillery fire support to the Iraqi army against IS.

According to analysts, this risk will increase if the US deploys Apache attack helicopters to the battlefield as planned to support the Iraqi army attacking Mosul in the coming months.

President Obama also recently approved an increase in troops deployed to Iraq to act as advisors and support forces for this country’s security forces.

`US advisors will continue to remain behind the front lines, but the challenges and risks to them will increase significantly as Iraqi troops and Kurdish militias move deeper into IS-controlled territory,` the official said.

See more: US special forces – the spear thrust into the heart of IS