An Iraqi federal police commando leader said at least six "Islamic State" (IS) militant suicide vehicle bombs had failed to deter Iraqi troops from advancing toward Mosul's old western city center.
"This is disgusting", Lise Grande, the humanitarian co-ordinator in Iraq said in the statement, "there is never justification - none whatsoever - for the use of chemical weapons".
On Saturday, the UN's humanitarian coordinator in Iraq, Lise Grande, said the alleged use by IS of chemical weapons earlier this week in an eastern district was "horrible".
ISIS has used chemical weapons in Iraq and Syria at least 52 times according to a report published late a year ago by IHS conflict monitor, a London-based research and intelligence gathering group.
Twelve people, including women and children, are being treated for possible exposure to chemical weapons agents in Mosul, where Isis is fighting off an offensive by US-backed Iraqi forces, the United Nations has said.
The total number of civilians displaced from Mosul has risen sharply over the past days and now exceeds 200,000, according to the International Organization for Migration (IOM).
However, west Mosul, with its narrow streets and a heavy population of between 750,000 and 800,000, appears to be a bigger challenge to the Iraqi forces, according to United Nations estimates.
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After more than two years of slow territorial victories against ISIS by Iraqi ground forces backed by USA -led coalition air power, western Mosul is the last significant urban area ISIS controls in Iraq.
The army launched an offensive to retake west Mosul on 19 February but bad weather has slowed the progress of Iraqi troops in recent days.
Isis fighters had "some mortar [teams] and snipers positioned inside homes", said Maj Ali Talib of the Iraqi special forces, explaining that US-led coalition airstrikes had helped destroy some of the Isis defences, but clashes were ongoing.
The Red Cross did not say who was to blame for the potential attack.
IS overran large areas of both countries in 2014, declaring a "caliphate" in territory it controlled, but the jihadist group has since lost ground to Iraqi forces and faced advances from different groups in Syria. The families are being held against their will in a camp functioning as an open-air prison near Tikrit. "In some cases we believe it had to do with land disputes".
"In discussions with tribal leaders they said they had the same plan", she said. Some of the men were asked to take off their clothes to prove they were not wearing explosive vests.