BAGHDAD, April 2 (Xinhua) -- Iraqi authorities discovered Monday the remains of 158 bodies believed to belong to soldiers of Speicher Camp who were executed by the Islamic State (IS) militants when the group seized Tikrit in June 2014, the Iraqi government said.

A joint team from forensic office and Iraqi Martyrs Foundation, tasked with registering martyrs before and after 2003 U.S.-led invasion to compensate their families, found the bodies inside a former presidential complex of the former Iraqi leader Saddam Hussein in the city of Tikrit, the forensic office affiliated with the Iraqi Health Ministry said in a statement.

The team exhumed the 158 decomposed bodies and began DNA testing to identify the victims, the statement quoted Zaid Ali, head of the forensic office, as saying.

Another mass grave inside the complex was found, Ali said, adding that the team will work on it later.

So far, the health ministry has handed over 704 martyrs of Speicher massacre to their families, according to the statement.

The discovered bodies believed to be part of 1,700 soldiers who walked out of an air base, known as Camp Speicher, north of Tikrit, some 170 km north of the Iraqi capital Baghdad, but were abducted and then killed by IS militants and some Sunni tribesmen.

In June 2014, armed Sunni insurgents, spearheaded by the IS group, launched a surprise offensive on Iraqi security forces and captured a large part of the country's northern and western territories after government troops abandoned their posts and military equipment.

The IS group later posted video footage and images showing the execution of Iraqi government soldiers.

After Iraqi security forces recaptured Tikrit from IS militants in April 2015, authorities, including forensic teams, worked at several mass graves and unearthed hundreds of bodies, many in military uniforms or with military identity cards.