Iraqi troops have a foot inside Mosul.

After a pause in the offensive to claim the key city back from Islamic State fighters because poor weather, Iraqi elite brigades fought their way into the outer suburbs of the city, searching house by search.

They were supported by air strikes.

A BBC journalist says the troops are moving with caution, amid fears of ambushes, secret tunnels and booby traps. Those militants who chose to stand and fight were killed, while others fled deeper into the city.

Video: Air strikes on Mosul help breach Islamic State group's defences – FRANCE 24 https://t.co/sjLoiFiqob

— France Top Daily (@FranceTopDaily) November 2, 2016

A television building has been seized, with one Iraqi commander saying the “true liberation” of Mosul had started.

Civilians are reported to have crowded into battered trucks and sedans on the road from Bazwaya, waving white flags and looking both relieved and bewildered.

Moving thru E area of #Mosul taken by #Iraq SpecF, so many children on the street waving – ppl smoking cigarettes, women showing their faces pic.twitter.com/J5exC6EFBq

— Joan C Soley (@JoanSoley) November 2, 2016

Earlier the Iraqi special forces held their positions along Mosul’s eastern outskirts as poor weather hampered visibility.

Brigadier General Haider Fadhil said high humidity and clouds were obscuring the view of aircraft and drones – a key component to the operations provided by a US-led air campaign.

#Iraqi airstrikes killed 116 #ISIS fighters including dozens in a pool of 5-star hotel in Mosul considered headquarters of the organization. pic.twitter.com/1Rxob18QE0

— Eli Dror (@edrormba) November 2, 2016

The pause came a day after Iraqi troops set foot in the city for the first time in more than two years, gearing up for urban warfare expected to take weeks, if not months.

Iraqi special forces had paused their offensive, when poor weather hampered visibility. Photo: AP

There are still more than one million civilians trapped in the city.

Wolfgang Gressmann of the Norwegian Refugee Council said its staff were “now bracing… for the worst” as the battle for the city intensified.

Mosul is the last major IS stronghold in Iraq, and driving the militant group from the city would be a major blow to IS ambitions of creating a cross-border “caliphate” stretching into Syria. IS announced the project in Mosul in 2014, after it routed the much larger Iraqi military, which had been neglected and demoralised by corruption.

However, concern over the fate of civilians caught up in the fighting has been growing, after residents reported that IS militants were rounding up thousands of residents to use as human shields and killing those with any suspected links to the security forces.

In one such account made to The Associated Press, the fighters went door to door in villages south of Mosul, ordering hundreds of people at gunpoint to march north into the city, where urban fighting is expected to be heaviest.

An Iraqi special forces soldier stands atop a Humvee in the village of Bazwaia, eight kilometres from the centre of Mosul. Photo: AP

In the latest international condemnation of IS, which has carried out mass killings of perceived opponents in the past and boasted about them in grisly photos and videos circulated online, the United Nations called on authorities to collect evidence of IS abuses of civilians for future use by tribunals.

Adama Dieng, special adviser to the UN Secretary-General Ban Ki-moon on the prevention of genocide, also expressed concern over “the increasing risk” of sectarian violence or revenge attacks during the Mosul campaign, especially where state-sanctioned Iraqi Shi’Ite militias are approaching Sunni communities.

“Any kind of retaliatory violence against individuals on the basis of their membership of a specific group is unacceptable and will undermine the legitimate calls of these communities for their own protection and for their long-standing grievances to be addressed,” he said in a statement released on Tuesday.

– with agencies