BAGHDAD/UNITED NATIONS - Fighters from the Islamic State group killed at least 18 members of two families as they attempted to flee the besieged militant bastion of Fallujah, relatives said on Sunday.

IS has been using civilians as human shields to defend its stronghold since Iraqi forces launched a vast offensive on May 22-23, on multiple occasions shooting those who tried to escape.

Iraqi military operations in the north and south-east of Mosul are causing fresh displacements, the United Nations refugee agency said Sunday, while pointing out that more than half a million people remain uprooted from their homes two years after fleeing violence in that city.

At the regular bi-weekly news briefing in Geneva, William Spindler, spokesperson for the Office of the UN High Commissioner for Refugees (UNHCR), said that more than 14,000 displaced Iraqis have been registered in camps north and south-east of Mosul – Iraq's second-largest city – and across the border in Syria, since the Iraqi Security Forces began a new military offensive in late March.  “Many of those who had fled the city two years earlier have had to move several times in search for safety and a decent place to live,” Spindler said, adding that most faced economic hardship.

He noted that a recent survey has found that unemployment is the greatest problem faced by families uprooted from their homes and scattered across Iraq, a country where more than 3.3 million people – around 10 per cent of the population – have been displaced due to conflict since the start of 2014.

Civilians who reached the safety of displacement camps south of the city and several aid organisations have reported cases of residents being shot dead, mostly as they tried to cross the Euphrates River to reach Iraqi government forces. In the worst known case so far, IS fighters killed at least 18 members of two families Friday as they attempted to flee, southeast of the city, relatives and a security officer told AFP by phone.

“A number of residents were trying to flee and as they neared the Al-Salam intersection, Daesh (IS) opened fire on them, killing 18 and wounding dozens,” a senior officer at the Joint Operations Command told AFP.

The officer, speaking on condition of anonymity because he is not authorised to talk to the press, said the army was able to rescue some of the wounded.

Relatives said the initial group that tried to sneak out of IS-controlled areas on Friday included around 100 individuals, including a majority of women and children.

The group were all from the same two families - Albu Hatem and Albu Saleh - and had made a previous failed attempt to leave days earlier.

“When they got near the intersection, which is the meeting point with the Iraqi forces, two gunmen on motorbikes arrived and sprayed them with gunfire,” said Ahmed al-Ghneim, a relative.

Two of the survivors, relatives from the Albu Saleh family, are staying at his home in Amriyat al-Fallujah, south of Fallujah. “Some of the residents jumped into the canal, some fled to a nearby house. When they entered it, it blew up on them because it was booby-trapped,” he said. “Some survivors were forced to go back inside Fallujah. Daesh took 17 of the wounded to Fallujah hospital,” Ghneim said.

Sami Abu Hatem, a relative who was already living in a camp in Amriyat al-Fallujah, confirmed that version of events. “Three of my direct relatives, a man with two young children, were among those massacred,” he said.

Abu Hatem he said he knew of 18 members of the group being killed and added that more were feared missing after jumping in the nearby canal.

According to aid groups running displacements camps outside Fallujah, only small numbers of residents have managed to flee the city centre.

Meanwhile, Iraqi troops advanced against Islamic State south of Mosul on Sunday as the US-led coalition intensifies its campaign against the militants on multiple fronts across their self-proclaimed caliphate.

Officers involved in the operation said Iraqi forces had moved towards the village of Haj Ali in tanks and armoured vehicles under cover of coalition airstrikes and artillery fire, capturing another village on the way.

“In the beginning they resisted but when they saw the force they withdrew,” said an Iraqi officer speaking from the newly recaptured village of Kharaib Jabr, adjacent to Haj Ali.

Haj Ali sits on the eastern bank of the Tigris river, opposite the Islamic State hub of Qayara, where there is an airfield that is set to serve as a staging ground for future operations to recapture Mosul, about 60 km (40 miles) north.

Islamic State overran Mosul two years ago and went on to proclaim a caliphate straddling Iraq and Syria but has come under increasing pressure in recent months, losing ground to an array of forces.

Iraqi forces are also advancing on the edge of the Islamic State bastion of Falluja further south, while in Syria US-backed forces are encircling the militant-held town of Manbij.

Iraqi troops were deployed to the northern Makhmour area earlier this year and launched an operation in March touting it as the beginning of a bigger campaign to retake Mosul - the largest city under militant control.

Since then, Iraqi forces have made modest gains, capturing a handful of villages on the eastern bank of the river Tigris.

The commander of the operation blamed the slow pace on a lack of tanks and said he did not have enough men to hold ground after it was retaken from the militants.

Last week, Iraq deployed an armoured division along with boats and bridges to cross the river to Qayara, control of which would also isolate Mosul from territory the militants control further south and east.

Meanwhile, the Iraqi army said on Sunday it had secured the first safe exit route for civilians to leave Islamic State’s besieged stronghold Falluja, and a Norwegian aid group said thousands of people had already used it to flee in the first day it was open.

Iraq has launched a major operation to recapture Falluja - an Islamic State bastion just an hour’s drive from Baghdad - but the United Nations fears for the fate of up to 90,000 civilians believed trapped inside with little food or water.

The new exit route, known as al-Salam (Peace) Junction, was secured on Saturday, southwest of Falluja, Joint Operation Command spokesman Brigadier Gen. Yahya Rasool told Reuters.

“There were exit routes previously, but this is the first to be completely secured and it’s relatively safe,” said Rasool.

About 4,000 people had fled the city over the past 24 hours through the al-Salam Junction, said Karl Schembri, a spokesman in Iraq for the Norwegian Refugee Council, which has been assisting people who escape the city.

“We expect thousands more to be able to leave in the coming days,” he said.

The al-Salam Junction route was secured after troops dislodged insurgents from districts located on the western bank of the Euphrates river, opposite Falluja’s city centre on the east bank, said Rasool. He did not give a number for the civilians who were able to flee so far using it.

More than 20,000 people have managed to flee the city and its surrounding area since the Iraqi army began the offensive on May 23, the United Nations said on June 8.

But the lack of secure routes made their escape extremely difficult and dangerous. At least a dozen people were reported to have drowned while crossing the Euphrates.

Those who managed to reach government-held lines said they walked for days to avoid sniper fire and explosive devices planted by Islamic State insurgents along roads to delay the army’s advance.

A government official said the militants were putting up a tough fight defending the city, long an insurgent bastion where US forces fought the heaviest battles of their own 2003-2011 occupation.

Prime Minister Haider al-Abadi says the troops are progressing cautiously in order to protect the civilians.

The army is receiving air support from the US-led coalition and ground support from Iranian-backed Shi’ite militias and Sunni tribal fighters.

The Shi’ite militias have deployed behind the army’s lines and did not take part directly in the assault on the city to avoid inflaming sectarian feelings.

The assault on Falluja is taking place at the same time as advances by US-backed fighters and Russian-backed Syrian government forces in Syria, at the opposite end of Islamic State’s self-declared caliphate.