Iraqi and coalition forces have faced little resistance and regained several villages from the so-called Islamic State since yesterday as they advance towards Mosul.
On the southeastern front line, the ninth armored battalion of the Iraqi government forces advanced at least 15km, retaking control of several villages in the south of Mosul.
As the troops moved forward, damaged houses and fallen utility poles could be seen scattered along the road toward the city.
The US-led coalition is providing air and ground support to tens of thousands of Iraqi army and Kurdish Peshmerga forces who launched the offensive yesterday to retake Mosul, the last major Iraqi city held by IS.
Kassem Jasem, commander of the ninth armored division, said militants were still carrying out occasional raids on the government troops with shoulder-fired missiles.
"Mosul will be a difficult fight. There will be advances and there will be setbacks," US President Barack Obama told a joint news conference with Italian Prime Minister Matteo Renzi on day two of the operation in northern Iraq.
Iraqi federal forces moved deep into Qaraqosh earlier, a town that lies around 15km southeast of Mosul and was seized by IS militants in August 2014.
Earlier, IS vowed to "defeat America" in a video claiming to show jihadist fighters patrolling the streets of Mosul after the launch of the offensive.
The video released today by the IS-linked Amaq news agency showed masked fighters in battledress patrolling a deserted, dimly lit thoroughfare in what it said was Mosul.
A masked fighter addressed the camera and said the United States would be defeated in Iraq.
"As for you, America, we promise you ... America will be defeated in Iraq and will leave, God willing, again - humiliated, wretched, dragging its tail in defeat," the fighter said.
There was no way to independently verify the contents of the video.
A spokesman for the US military confirmed that the international coalition carried out air strikes in Mosul "to soften up" militant-held areas ahead of the ground offensive.
Iraqi security forces were "ahead of schedule" after the first day of the offensive a Pentagon official said last night.
"Early indications are that Iraqi forces have met their objectives so far, and that they are ahead of schedule for this first day," Pentagon press secretary Peter Cook said.
But he warned it was unknown how long the battle would last. A top US general earlier said it would take several weeks or even longer.
The UN Humanitarian coordinator for Iraq has said it is "running against the clock" in order to prepare a number of emergency sites where civilians, fleeing violence in Mosul, can be housed.
Speaking on RTÉ's Morning Ireland, Lise Grande said that, in the worst case scenario, up to a million civilians will flee the city with at least 700,000 of them needing shelter and support.
She said that six sites are ready but at least 20 more are needed.
Ms Grande added that there was tent capacity for 400,000 people but that they do not have the areas to put them in.
"What we've been doing is identifying, with the government, areas - emergency sites - where these people can be housed," said Ms Grande.
"Right now, as the operation begins, six of those sites are ready. They can start taking people. We are running against the clock trying to prepare more than twenty additional sites."
