In a significant escalation of the battle for Mosul, elite Iraqi special forces have joined the fight, unleashing a pre-dawn assault on an Islamic State-held town east of the besieged city, as the US military announced the first American combat death since the operation began.
US officials said the American service member died on Thursday from wounds sustained in a roadside bomb explosion north of Mosul.
More than 100 US special operations forces are embedded with Iraqi units in the offensive, and hundreds more are playing a support role in staging bases.
The American had been advising members of the Iraqi Kurdish force known as the peshmerga, a US official said, speaking on condition of anonymity because he was not authorised to publicly discuss details.
Roadside bombs and other improvised explosive devices pose a particular danger to advancing Iraqi forces and the US advisers who are with them.
The Islamic State group, which has occupied Mosul for more than two years, has prepared extensive defenses in and around the city.
As they charged toward the town of Bartella, 15 kilometres from Mosul's outskirts, the Iraqi special forces faced another favoured weapon in the IS arsenal: armoured trucks packed with explosives and driven by suicide bombers.
The militants' signature battlefield tactic, the weapons offered a glimpse at what Iraqi forces can expect as they close in on the extremists' biggest urban bastion.
The pre-dawn assault on Bartella was part of a multi-pronged operation on eastern approaches to Mosul, Iraq's second-largest city. Attack helicopters strafed militant positions as they advanced amid a hail of gunfire.
The US-trained special forces, officially known as the Counter Terrorism Service, are widely seen as Iraq's most professional and least sectarian fighters, and have served as the shock troops in previous campaigns against IS.
They are expected to lead the charge into Mosul.
Mosul is home to more than a million people, and rights groups fear a potential humanitarian crisis.
Meanwhile, Prime Minister Haider Al-Abadi said Mosul may fall sooner than expected. The campaign to retake the city, which began Monday, had been expected to last weeks, if not months.
Speaking by video transmission to a conference in Paris focused on post-liberation planning for Mosul, the Iraqi leader said the Iraqi "forces are currently pushing forward ... more quickly than we thought, and more quickly certainly than we established in our plan of campaign."
The Islamic State group captured Mosul and the surrounding area during a lightning advance across northern Iraq in the summer of 2014, and IS leader Abu Bakr al-Baghdadi announced the formation of a self-styled caliphate from the pulpit of a Mosul mosque.