Kimberly Rivera, an American soldier who moved to Canada to avoid the Iraq war, has been deported to the U.S.

The mother of four presented herself at the Canada-U.S. border in Gananoque, Ont. on Thursday, where she was arrested and transferred to U.S. military custody.

“Kimberly now awaits punishment for refusing to return to Iraq, a conflict which Kimberly and Canada determined was wrong,” the group War Resisters Support Campaign said in a statement.

Rivera’s husband and children, two of whom were born in Canada, crossed the border separately on Thursday, according to the group’s spokesperson.

"She didn't want her children to see her arrested by the military," said Ken Marciniec.

The parliamentary secretary to Immigration Minister Jason Kenney confirmed the deportation in the House of Commons, drawing a huge cheer from the Conservative benches.

"Our government does not believe that the administration of the president or the president himself in any way, shape, or form, is going to persecute Ms. Rivera,” said Rick Dykstra, Conservative MP for St. Catharines, Ont.

While Rivera’s supporters were hoping for a last-minute intervention by the government, news of the 30-year-old’s deportation sparked a series of protests across the country.

The largest one was in Toronto, where Rivera has been living with her family since she moved to Canada in 2007.

Some 20,000 people also signed an online petition protesting the deportation order.

According to the War Resisters Support Campaign – a group founded by U.S. war resisters to help those seeking asylum in Canada – Rivera faces the likelihood of court martial and imprisonment for leaving the U.S. to avoid further military service.

"No one should go to jail in any country, anywhere in the world, for conscientious objection to war," Marciniec told The Canadian Press.

"It's important for our government's treatment of Iraq war resisters to catch up with the opinion of the majority of Canadians on this issue."

Rivera's deportation was called an "international tragedy" by the United Steelworkers on Thursday.

"This gives Canada a black eye on the international stage. Our country's once-proud tradition as a safe haven for conscientious objectors has been destroyed with Kim's deportation," national director Ken Neumann said.

"Immigration Minister Jason Kenney had the opportunity to show compassion and do the right thing, and he refused to act."

Rivera has applied to become a permanent Canadian resident on compassionate grounds. A decision is pending.

Rivera told reporters in Toronto last month that she has always opposed the Iraq war and even stopped carrying a gun while deployed overseas.

She said she fears being separated from her children, two of whom were born in Canada, if she is sent back to the U.S. and faces jail time.

Rivera’s lawyers argue that her outspoken criticism of the Iraq war is likely to get her in hot water at home, suggesting critical soldiers have been punished in the past.

On Monday, a federal court judge denied her request for a stay of removal, finding the possibility of her arrest and detention in the U.S. to be speculative.

With files from The Canadian Press