As fighting to recapture Mosul entered its third day, Iraqi forces advanced on the city as US-led coalition air strikes pounded the nearby town of Hamdaniya.
The addition of the elite troops marks a significant intensification of the fight. Iraqi Army spokesman Brigadier Yahia Rassoul said there have been more than 20 suicide cars trying to target army vehicles during the advance, but they were all destroyed.
Earlier this month, a Canadian general who runs a portion of the coalition training of Iraqi security forces told reporters that retaking Mosul from the Islamic State would open a new, more risky phase of the counter-IS fight.
"We are working to increase this number of tents in the coming days", he said.
Russian warplanes in neighboring Syria have been carrying out airstrikes for more than a year in support of Syrian forces.
Iraqi forces say they have captured 10 villages near Mosul since beginning their long-awaited offensive on Monday.
The Kurdish forces known as peshmerga, who are also taking part in the offensive, announced a "large-scale operation" to the north and north-east of Mosul on Thursday.
"Make no doubt the Iraqi security forces have the momentum", U.S. Army Gen Gary Volesky, commander of Operation Inherent Resolve's ground forces, said Wednesday, adding that coalition forces must continue to apply "unrelenting pressure on the enemy and then the enemy's going to break".
A senior military commander says Iraqi special forces have driven Islamic State militants out of a town east of Mosul.
This suggests that a military victory over the IS will not suffice, and the Mosul operation would be a test of the Iraqi government's capacity to mend the sectarian conflict that enabled the rise of the IS in the first place.
Coalition forces expect IS to have laid a series of booby traps in and around Mosul as part of their effort to hamper Iraqi advances.
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"We are very anxious about the safety of innocent civilians in Mosul city", Su'ad Jarbawi, Iraq country director for Mercy Corps, a humanitarian aid agency, said in a statement.
That could allow Islamic State fighters in Mosul to regroup in Syria, neighboring countries or Europe.
"We've even seen them rig a full oil tanker with explosives", he said.
A unit of what appeared to be United States special forces advisers entered ISIS territory with the very first armored convoy of Peshmerga on Monday, a CNN team observed. They have led the assaults on Ramadi and Fallujah over the past year.
On Monday, Iraqi troops-along with Peshmerga fighters and a Christian paramilitary group-launched a major offensive to take back the Iraqi city of Mosul from ISIS.
Lt. Gen. Talib Shaghati told reporters at a military base that up to 6,000 IS fighters are inside the city.
The special forces are expected to lead the way into the city itself, where they will face fierce resistance in an urban landscape where IS militants are preparing for a climactic battle. These militias have threatened to attack USA troops fighting in Iraq and stall their efforts against the Islamic State if they come into contact with Americans.
Forces have been approaching from the south, east and northeast - cutting off potential escape routes for terrorist operatives - and US air support has made militants' flight even more unlikely.
As many as 5,000 ISIS fighters are believed to remain in the city.
The force proved to be a more reliable partner to the Americans than the mainstream security forces, where corruption was rife and many units were tied to parties or militias. The deployment of US attack helicopter crews brings added risk for American troops.