Two boys kidnapped by their mother

Two brothers allegedly kidnapped by their biological mother and taken to Mexico six months ago have been reunited with their father.

Sage Cook, 15, and Isaac Cook, 9, disappeared in August after visiting their biological mother, Faye Ku, in Lakewood, California, local authorities said in a statement.

Before they vanished, the boys lived in Bellevue, Washington, with their father, the FBI said in a statement Friday. Their father, David Cook, got custody of the children after he and Ku divorced seven years ago, police said.

"Authorities located them in safe condition in Mexico's Sinaloa state," the FBI's Seattle Division said.

"This evening, they returned to Washington with their father, David Cook, and stepmother, Helen Cook, after being reunited in Mexico."

Mother left behind a letter

Investigators allege Ku, 41, crossed the border from San Diego to Tijuana, Mexico, with the children on August 29.

"Ms. Ku intentionally left behind personal belongings at her place of residence that would prevent law enforcement from tracking her whereabouts," Lakewood Sheriff's Station said.

"In a prepared a letter, she blamed the children's father for trying to control them, and asked him to leave them alone."

Federal custody

The biological mother has been deported from Mexico and taken into U.S. custody, the FBI said. She is expected to appear in the U.S. District Court in Los Angeles on Tuesday.

Authorities said Ku made another attempt to leave the country with the children three years ago, but she was detained before boarding a flight to Taiwan.

She has been charged with international parental kidnapping.