Britain will boost the number of its army trainers in Iraq in the coming weeks to support the Iraqi armed forces' battle against Islamic State militants, the British defence secretary said on a visit to Baghdad on Wednesday.

Britain said last month it had deployed a team of trainers to Iraq to help Kurdish peshmerga fighters maintain and use heavy machineguns against the radical militants who have taken over much of Iraq and Syria in a ruthless military onslaught.

Britain planes have also participated in US-led air strikes against Islamic State, which has beheaded two British aid workers and two US journalists.

Defence Secretary Michael Fallon, who met top Iraqi government officials during his visit to Baghdad, said the details of the mission would be ironed out soon.

"We have a small number of people here. We will be looking now to see how we can strengthen that, the liaison work we are doing in the ministries and the security agencies here," Fallon told reporters.

"This is fairly urgent. We will be doing this in the next few weeks. That's what we have been asked to do."

The United States spent billions of dollars training and funding Iraqi security forces during the occupation of the country following Saddam Hussein's fall in 2003.

The quality of the training was called into question when several hundred Islamic State militants swept through northern Iraq in June, meeting little resistance.

The Iraqi army rapidly collapsed in the face of the onslaught, leaving behind weapons and tanks that the al Qaeda offshoot has been using in its attempts to expand a self-proclaimed Islamic emirate in Iraq and Syria.

Air strikes against Islamic State targets after the group started beheading Western hostages have slowed the militants' advance. But Iraqi and Western officials believe the group can only be defeated if Iraqi security forces improve their performance, and that will take time.

As well as the additional training, Fallon said Britain was looking to fill gaps in Iraqi military equipment.

"We'll be making further gifts of supplies: spares for machine guns, binoculars, first aid kits," he said during a visit to a firing range where British soldiers from the Yorkshire Regiment were training Kurdish peshmerga to use British machine guns.

"We are stepping up out commitment to training and supply of both weapons and ammunition."

Aside from a poor showing on the battlefield, sectarianism is hampering security forces.

Just outside the heavily fortified Baghdad zone where Fallon was speaking, soldiers openly displayed pins on their uniforms that revealed they were members of Iraq's Shi'ite majority.

Fallon said Britain would share expertise in roadside bombs and car bombs gained while fighting the Taliban in Afghanistan.

"We have some specialist knowledge to contribute there and we are going to see how we can help train the Iraqi forces directly in that," he said.

In recent days the insurgents killed more than 300 members of a Sunni tribe in western Anbar province.

The Iraqi government hopes the area will help the army to fight the insurgents and the United States wants both sides to revive an alliance that helped defeat al Qaeda during the US occupation.

However, mistrust between the Shi'ite led administration and the Sunni tribes runs deep. The Albu Nimr tribe said the government and army ignored repeated pleas for help as the Sunni insurgents approached their village.

Fallon said the Albu Nimr, who battled Islamic State for weeks, were an example of the resolve of tribesmen.

"Any casualties are regrettable. Even that shows you that the tribes are taking the fight to IS and they are determined to get IS out of their villages and out of their areas," he said.

Britain's strategy in Syria will remain far less intensive than that in Iraq, Fallon said.

"What we have done is stepped up our surveillance of Syria and we are looking at other ways of helping to train moderate Syrian forces, for example community self defence."

(Reuters)