MINNEAPOLIS (AP) - A man who authorities say played a key role in funneling young men from Minnesota to a terrorist group in Somalia was sentenced to 20 years in prison, while another man who was a foot soldier for al-Shabab received a 10-year sentence.

Mahamud Said Omar, 47, and Kamal Said Hassan, 28, learned their sentences on Monday as a federal judge in US District Court in Minneapolis began doling out penalties in what has been called one of the largest efforts to recruit US fighters into a foreign terror group.

Hassan is among the more than 20 young men who have left Minnesota since 2007 to join al-Shabab. Minnesota is home to the largest Somali population in the US.

Hassan pleaded guilty in 2009 to two terror-related counts and one count of lying to the FBI. He admitted he trained with the Al-Qaeda-linked group in Somalia and participated in an ambush of Ethiopian troops before returning to the US.

"I helped al-Shabab and I lied to the US government, your honour. I can't take back what I did, but I can show you and my family and the government and the Somali community that I can do better," a tearful Hassan told Chief US District Judge Michael Davis in Minneapolis before he was sentenced.

Hassan apologised during his 2.5-hour sentencing and said he no longer supports al-Shabab or any similar group. He faced a maximum of 38 years in prison, but the government sought a reduced sentence because Hassan gave "extraordinary" cooperation as authorities were building their investigation.

But Judge Davis said he is not convinced that Hassan is not still lying. The judge had a recruitment video played in court that shows Hassan urging others to join the cause in Somalia to show that Hassan can be persuasive.

"I don't know you. The government doesn't know you. Your family doesn't know you," Judge Davis told Hassan. Still, he said Hassan was the first person to come forward and shed a light on terror recruiting in Minneapolis, and he granted the lower sentence.

Hassan will also be on supervised release for 20 years after he is out of prison.

Authorities say the conspiracy began in 2007, when small groups of Somali men began holding secret meetings to talk about returning to their homeland to wage jihad against Ethiopians. The Ethiopian army was brought into Somalia in 2006 by its weak UN-backed government, but the troops were viewed by many Somalis as invaders.

Hassan has said he was told it was his "duty" to fight against Ethiopians.

Omar also made a lengthy statement before he was sentenced - much of it was incoherent and rambling. He denied taking part in the conspiracy, and said his attorneys were "disrespecting" him because they told him not to write the judge a letter.

During Omar's trial, prosecutors alleged Omar, a janitor at a local mosque, used recruits as "cannon fodder" and helped feed them into a pipeline of violence in their homeland. They said he continued to help travelers with logistics and money even in the days after a Minnesotan carried out a suicide bombing in Somalia in 2008. Prosecutors say most of men who left in that group of travelers have died.

Prosecutors had sought a sentence of 50 years in prison.

Omar's defense attorneys argued in court documents that he was a passive participant who didn't know any better and held no power.

"Mr Omar was a pawn who, because of his mental disabilities became involved in an organization whose evil was far more advanced than he could comprehend," defense attorney Andrew Birrell wrote.

Hassan, who was convicted on two terror-related counts and one count of lying to the FBI, has admitted that he went to Somalia to fight against Ethiopians, trained with al-Shabab and left after participating in an ambush of Ethiopian troops.

Prosecutors wrote that, to date, neither al-Shabab's designation as a terrorist group nor the prosecutions of men in the US have stemmed the flow of support from Minnesota.