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By Erik Ortiz

Three men accused of delivering "incendiary" speeches in support of ISIS and advocating for terrorism were convicted by a British court Tuesday following almost two years of an undercover operation.

The men — identified as Yousaf Bashir, 36; Rajib Khan, 38; and Mohammed Istiak Alamgir, 37 — belonged to the group Al-Muhajiroun, a banned terrorist network in Britain that has claimed support for an Islamic caliphate, according to the Bedfordshire and Metropolitan police.

The terror trio were living in Luton, about an hour north of London, authorities said.

Rajib Khan, 38 from Luton, England.Metropolitan Police

Police conducted an undercover investigation — dubbed Operation Weedproof — for 20 months and said they attended meetings at a Luton church and an associate's backyard where they spoke to around 50 to 70 people at a time, including children.

"The group praised (ISIS) and encouraged others to support the proscribed (organization), including by travelling to Syria to fight alongside them," police said.

Related: Anjem Choudary, Radical U.K. Preacher, Convicted of Urging ISIS Support

The men's messages were having an impact, according to investigators.

Metropolitan police later arrested two people who listened to those speeches and were influenced by them. One man was convicted of plotting to kill an American solider in the United Kingdom, and another was imprisoned for planning to join ISIS in Syria.

Investigators said they also found photos and videos of the men with Omar Bakri Muhammad, the founder of Al-Muhajiroun, and recordings of the men giving extremist speeches.

Bashir was found guilty of one count of addressing a meeting to encourage support for a proscribed organization.

Yousaf Bashir, 36, from Luton, England.Metropolitan Police

Khan was found guilty of one count of arranging, assisting in arranging or managing a meeting to support a proscribed organization and one count of addressing a meeting to encourage support for a proscribed organization.

Alamgir was found guilty of three counts of addressing a meeting to encourage support for a proscribed organization. He was also accused of collecting money at meeting to pay for the legal fees of Bakri Muhammed, who was sentenced to six years in prison by a Lebanese court for founding an affiliate of the al Qaeda-linked group the Nusra Front and building a training camp.

Commander Dean Haydon, head of the Metropolitan Police Counter Terrorism Command, said the speeches that Bashir, Khan and Alamgir were giving "inspire the terrorists of tomorrow" — and they needed to be shut down.

"The men used meetings about Ramadan — a time for self-reflection and change for the better — to instead deliver subversive speeches that encouraged groups, including very young children, to engage in war alongside (ISIS)," Haydon said in a statement.

A sentencing date for the men has yet to be set.