Iraq has promised to recapture Mosul by year's end and US top brass have hinted an operation could start next month, but the offensive to retake the jihadist bastion faces serious challenges.
Mosul, Iraq's second city, is the ultimate prize in the country's war against the Islamic State group, which seized it and swathes of other territory in 2014.
But before Iraqi forces can enter and retake the city, there are an array of complex military, political and humanitarian challenges to surmount, meaning that even if the operation begins next month, it is likely to take weeks or months to complete.
In the battle for Mosul, there will be "formidable challenges at all levels, one of the most important of them coordination between military units taking part in the battle," said Iraqi security analyst Jassim Hanoon.
The drive will involve Iraqi soldiers and police, pro-government paramilitaries and fighters -- forces that in some cases have not operated together before and do not have unified command structures.
Senior US officers have spurred much of the recent speculation on when the final push for the city will start, while Prime Minister Haider al-Abadi has said he wants to maintain surprise.
Chairman of the Joint Chiefs of Staff General Joe Dunford, said that Iraqi forces will be ready for the push by "early October", while General Joe Votel, the head of the US Central Command, said the city can be retaken by year's end.
- Humanitarian challenges, rival forces -
But there are still serious humanitarian challenges to be addressed, with the United Nations saying that: "Humanitarian agencies are racing against the clock to prepare for the humanitarian impact of the military campaign."
Once the push is launched, a coalition of heterogenous and sometimes rival Iraqi forces will have to fight through IS defences -- in some cases over distances of dozens of kilometres (miles) from their current positions -- to reach the city.
Then, if Iraqi strategy for Mosul follows that used in previous operations, they will seek to surround and seal off the city prior to an assault.
Following reports of a possible mustard agent attack on US troops south of Mosul on Tuesday and confirmed chemical weapons attacks on Kurdish forces in the past, there are also concerns that IS might resort to such tactics in its defence of the city.
US-led coalition warplanes last week destroyed a factory near Mosul suspected of being used by IS to make chemical weapons.
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But chemical weapons attacks have so far resulted in limited casualties, and IS's bombs and bullets are much deadlier weapons.
- Operations already begun -
Dunford said the timing of the Mosul operation "now is really just a function of a political decision by Prime Minister Abadi," but in reality the situation is far more complex.
Kurdish forces will play a major role in the operation, and they are not under Abadi's command, meaning that a decision by the Kurdish regional government is also needed.
That will require an agreement, or at least some initial understanding, between Baghdad and the Kurds on a post-Mosul division of territory.
The Kurds want to maintain control of a number of areas that are also claimed by Baghdad.
The role of paramilitary forces known as the Hashed al-Shaabi (Popular Mobilisation), which are dominated by Iran-backed Shiite militias, must also be decided.
These forces are ostensibly under Abadi's control, but in practice the most powerful groups operate with a great deal of autonomy and with input from Tehran.
Their entry into Sunni Arab Mosul is opposed by Sunni politicians.
While there has been much recent discussion about the launch of the drive on Mosul, operations to prepare for it began months ago.
Iraq announced in March that it had launched the offensive to retake the city, and the top US envoy to the coalition, Brett McGurk, has said several times that the Mosul operation was already under way.
Even after Mosul is retaken, the war against IS will be far from over.
The jihadists are likely to revert to insurgent tactics, such as bombings of civilians and hit-and-run attacks on security forces, following the demise of their "state" in Iraq.