BAGHDAD -- Iraqi forces battled Islamic State fighters for a third day in a remote western town far from Mosul on Tuesday, but the U.S.-led coalition insisted the latest in a series of "spoiler attacks" had not forced it to divert resources from the fight to retake Iraq's second-largest city.

Iraqi Prime Minister Haider al-Abadi acknowledged that the militants briefly seized the local government headquarters in the western town of Rutba, offering new details about the assault, which U.S. and Iraqi officials have sought to downplay since it began on Sunday.

The White House envoy to the U.S.-led coalition battling IS insisted the militants' strategy was failing, saying there had been "no diversion whatsoever" of forces taking part in the Mosul operation, which is expected to take weeks, if not months.

"Daesh is trying to launch spoiler attacks," Brett McGurk told reporters at a Baghdad news conference, using the Arabic acronym for IS. "This was expected, it's planned for, and we can expect more of it."

The complex assault on Rutba, located hundreds of miles (kilometres) south of Mosul, is just the latest IS attempt to try to divert Iraqi military resources from the fight for the militants' last major urban bastion in Iraq. Last week the group launched a similar attack in and around the northern city of Kirkuk, some 100 miles (170 kilometres) southeast of Mosul, igniting gun battles that lasted two days and killed at least 80 people.

McGurk said the militant attacks on Rutba were carried out by "small, isolated teams" and were "easily defeatable." But he acknowledged there was still a "small Daesh presence" in two neighbourhoods.

The Iraqi military has insisted throughout the Rutba assault that the situation is under control, without offering further details.

Al-Abadi acknowledged Tuesday the militants did have some initial battlefield successes at the start of the offensive Sunday. "They took control, it's true, of the municipal headquarters," the Iraqi prime minister told reporters. But he said Iraqi security forces drove them out "within hours" and had regained control of the town.

However, Rajeh Barakat, an Anbar provincial councilman who sits on the security committee, said earlier Tuesday that IS fighters were still clashing with security forces in two southern neighbourhoods of Rutba.

"We have reports saying the militants killed some civilians and members of the security forces, but we don't know how many," he said.

Near Mosul, fighting continued Tuesday in a belt of villages and towns to the north, east and south of the city. Maj. Gen. Haider Fadhil said the Iraqi special forces had reached a village some four miles (six kilometres) from the eastern edge of Mosul.

Around 335 civilians were evacuated to a refugee camp from the village of Tob Zawa, about nine kilometres (5 1/2 miles) from Mosul, which was retaken by special forces on Monday, Fadhil said. He said the civilians were relocated to protect them from possible IS shelling.

Among them was Ezzat Shaheen, who drove his car along with his wife and some of his 10 children. Others were left behind to take care of their land and cattle.

"To be honest, our life (under IS) was good," the 55-year-old Shaheen said. "There was justice. There were clear principles -- such as don't shave your beard and pray in the mosque."

"If you don't violate them, no one will (bother) you," added Shaheen, who sported a full white beard.

Others who have escaped the Mosul area have described harsh conditions under militant rule, saying the fighters imposed religious and military training on children and forced people to attend daily prayers.

Abdeljabar Antar, who was among those evacuated from Tob Zawa along with his wife and four children, said the IS militants had included foreign fighters "who spoke languages I don't know -- Russians, Pakistanis."

In the days before the offensive, Antar said the village ran low on food and supplies, and residents had to get permission from IS to leave.

"I hope life will return to the way it was before 2014," he said, referring to the summer when IS militants swept across northern and central Iraq, capturing Mosul and surrounding towns.

The IS-run Aamaq news agency, meanwhile, released a video purporting to show a missile attack on an Iraqi Abrams tank near Qayara, to the south of Mosul. The footage, which carried a date stamp indicating it was shot Monday, showed what appeared to be a shoulder-fired missile hurtling toward the tank from behind at fairly close range, blowing it up and igniting a massive fireball.

The U.S.-led coalition, which has been carrying out airstrikes in support of the Mosul operation, said five on Monday destroyed 22 fighting positions, eight tunnels and nine vehicles, one of which was rigged with explosives.

The U.S. is also providing ground support, with more than 100 American soldiers embedded with Iraqi units and hundreds more working in staging bases. A U.S. soldier taking part in the operation was killed by a roadside bomb last week.

Abdul-Zahra reported from Tob Zawa, Iraq. Associated Press writers Sinan Salaheddin and Ahmed Sami in Baghdad contributed to this report.