Isis is allegedly attacking Iraqi soldiers with roadside bombs containing chlorine gas as allied forces continue a huge assault against the group in Tikrit.

Footage captured by an Iraqi bomb disposal team shows plumes of thick orange gas emerging from a detonated roadside bomb.

The team told the BBC it has diffused “dozens” of chlorine bombs left by Isis militants, which it says are used more as a means to create fear than harm.

“They have resorted to this new method. They are putting chlorine inside these homemade roadside bombs, which is toxic for those who inhale it,” Haider Taher, a member of the bomb disposal team, said.

It is not the first time claims have emerged that the group uses bombs filled with chemical agents. In October last year, Kurdish officials and doctors said they believed toxic gases had been released in an eastern district of Kobani.

The bombs are being used as Iraqi soldiers and allied Shia militiamen backed by local Sunni tribes continued their offensive to reclaim Tikrit from the clutches of the extremist group.

In pictures: Fight for Tikrit Show all 16 1 /16 In pictures: Fight for Tikrit In pictures: Fight for Tikrit Fight for Tikrit Shiite fighters pose in front of a mural depicting the emblem of the Islamic State group outside one of the presidential palaces in Tikrit, on April 1, 2015 Getty Images In pictures: Fight for Tikrit Fight for Tikrit Iraqi Prime Minister Haider al-Abadi tours the city of Tikrit after it was retaken by the security forces in Baghdad, Iraq, on April 1 2015 AP In pictures: Fight for Tikrit Fight for Tikrit An Iraqi flag waves over the Tigris River om April 1 2015 AP In pictures: Fight for Tikrit Fight for Tikrit Iraqi security forces playing football in Tikrit after their country declared a 'magnificent victory' over the Islamic State group in the city on April 1 2015 Reuters In pictures: Fight for Tikrit Fight for Tikrit A member of the security forces holds Iraq’s national flag in front of a painted Isis emblem Getty Images In pictures: Fight for Tikrit Fight for Tikrit Iraqi security forces arrest a member of the Islamic State in Tikrit on April 1, 2015 Reuters In pictures: Fight for Tikrit Fight for Tikrit A member from the Iraqi security forces beats an Isis insurgent, who was captured in Tikrit Reuters In pictures: Fight for Tikrit Fight for Tikrit Shiite fighters from the Popular Mobilisation units celebrate in front of the the provincial council building inside the northern Iraqi city of Tikrit on March 31, 2015 Getty Images In pictures: Fight for Tikrit Fight for Tikrit Iraqi soldiers stand on a damaged tank during fighting against IS militants near Tikrit Corbis In pictures: Fight for Tikrit Fight for Tikrit Fighters of Iraqi Shiite militias who volunteered to support the Iraqi forces make their way towards Daquq town near Tikrit Corbis In pictures: Fight for Tikrit Fight for Tikrit Iraqi security forces and Shia fighters chant slogans as they gather at Udhaim dam, north of Baghdad, where they have been massing in preparation for an attack on Isis along the Tigris River Reuters In pictures: Fight for Tikrit Fight for Tikrit Pro-government volunteer Shia fighters in Awaynat near Tikrit AFP/Getty In pictures: Fight for Tikrit Fight for Tikrit Iraqi government forces and allied militias firing weaponry from a position in the northern part of Diyala AFP In pictures: Fight for Tikrit Fight for Tikrit A volunteer in the Iraqi Shiite Badr Army militia taking up position outside Tikrit Corbis In pictures: Fight for Tikrit Fight for Tikrit Volunteers of the Iraqi Shiite Badr Army militia patrol an area at eastern Tikrit city Corbis In pictures: Fight for Tikrit Fight for Tikrit Members of the Iraqi security forces coming from the city of Samarra drive towards al-Dawr south of Tikrit to launch an assault against the Islamic State AFP/Getty

Tikrit, Saddam Hussein's hometown, was overrun by militants during Isis’s rapid advance across northern Iraq in June last year. Now, Iran is helping to co-ordinate the 20,000 soldiers attempting to drive out militants in the biggest assault led by the Iraqi Government yet.

Allied Iraqi forces first entered the Isis stronghold through its northern Qadisiyya neighbourhood, according to video obtained by The Associated Press. Iraqi officials say the offensive was aided by helicopters firing missiles from above, while another force pushed in from the south of the city.

Isis fighters were reportedly using civilian vehicles to try and flee the city.

Forces are now attempting to advance towards the centre of Tikrit. The US says coalition airstrikes are not involved in the operation to take back the city.