Amid heavy exchanges of gunfire and grenades between Iraqi soldiers and Islamic State (Isis) militants during the offensive in eastern Mosul, Shia soldiers are reportedly also engaging in a war of words with the Sunni militants.

"They chanted calling us rawafiz [apostates]," Ammar Hasan, an Iraqi soldier, told Rudaw. "And we chanted saying 'We are Ali-Shiites'."

Isis, which comprises of Sunni Muslims, considers Shias non-Muslims. There have been reports of Isis brutality on minority Shia Muslims living in Iraq and Syria. The ensuing hatred has driven Shia soldiers to seek revenge from the jihadists.

Hasan, who hails from the predominantly Shia city of Hilla in central Iraq, narrated his heated exchange with an Isis fighter during a gunfight to capture the site of the Prophet Jonah's tomb, which was destroyed by the militants in late 2014.

Narrating the incident, Hasan recalled: "He [the Isis militant] said 'I will behead you like a sheep'. I told him 'Woe, woe betide you. We are Ali-Shiites' and I threw a grenade and killed him."

Ahmad Jasm al-Zuhair from Karbala, Iraq, admitted to taking revenge from an Isis militant they captured alive. "We arrived here. They numbered about eight or 10," Zuhair said of an encounter with the militants on a street located in Nabi Younis district.

"They were chanting 'Allahu Akbar'. They were in that house, and we were in that one. We threw grenades at them. We killed two of them, and this one here was afraid. He surrendered," he said pointing at a dead body next to him.

Mosul offensive
Shia soldiers in the Iraqi army boast of revenge killings as they involve in war of words with Isis militants during gun fights in Mosul - File photo Reuters

"We shot a rocket at that house, and he turned himself in with his gun. But we took revenge for our friends and killed him," Zuhair added.

Yasr Hussein, another Iraqi soldier, said he too had a war of words with the militants: "We told them 'Ali is with us'," referring to Shia leader Ali ibn Abi Talib. "Who is with you?" Hussein reportedly told the militants.

The rift between Shia and Sunni Muslims goes back centuries and it is believed that they split when Sunnis chose to follow Abu Bakr as-Siddiq, after the death of the Prophet Muhammad, while Shias opted to follow Ali, Muhammad's cousin and son-in-law.

Some Shia soldiers are currently fighting against the terrorists as part of the elite Iraqi Counter Terrorism Service (ICTS) and are mainly concentrated in eastern and northeastern Mosul. A separate Iran-backed Shia militia – Popular Mobilisation Forces (PMF) – is also assisting Iraqi forces to rid the country of the terrorists.

The inclusion of Shia militias in the battle for Mosul was hindered initially – when the soldiers offered to liberate Isis stronghold Tel Afar in west Mosul – primarily because of their anti-Sunni stand.

Meanwhile, Iraqi forces announced on Wednesday (18 January) that east Mosul was liberated and they are now advancing towards west Mosul. The offensive in Iraq's second city began in October 2016.