Arthur Simpson-Kent, 48, was last questioned by police about Blake's disappearance in December, and had last been seen at the Kotoka International Airport in Ghana on Dec. 19.
"Detectives have today, Saturday, 9 January, been made aware of an arrest in Ghana," Scotland Yard said in a statement to PEOPLE.
"We are currently working alongside the Ghanaian authorities but are not in a position to discuss further at this time."
British police confirmed to The Guardian on Sunday that the man arrested was Simpson-Kent.
On Sunday, British police told PEOPLE that they were moving forward with extraditing the suspect to the U.K.
"An application for extradition will be made by officers and partner agencies in due course," Scotland Yard said in a statement.
Detective Chief Inspector Graeme Gwyn, of the Met's Homicide and Major Crime Command, said, "I would like to pass on my extreme thanks to the Ghanaian Police for their valuable assistance in this matter.
"Our thoughts remain with Sian and the children's family at that this time.
"We continue to work alongside the Ghanaian authorities and agencies in London to progress this investigation and are discussing the extradition process.
Detectives had made previous appeals for "any information" about Simpson-Kent's whereabouts and were actively searching for him, PEOPLE confirmed.
The bodies of Blake and her sons, 8-year-old Zachary and 4-year-old Amon, were discovered in the rear garden of their home in Erith, Kent, on Jan. 5 – some 20 days after police first began investigating their disappearances, following contact from the anti-child abuse charity NSPCC.
Postmortem examinations provisionally concluded that the former actress, 43, and her children died as a result of serious head and neck injuries.
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"She didn't want to throw him out on the street but give him time to find somewhere else to live," Ava said. "That was the only point she was wavering on."
Ava said she firmly believed Simpson-Kent was "responsible" for the deaths, and called on him to "answer to the courts of this country and to God."
"He was my nephews' primary caregiver," Ava said. "I still can't believe, not only that they're dead, but that he was capable of killing his children.
"My sister, I can understand up to a point. Maybe there was an argument – this is what I would like to believe – and maybe she has fallen and hit her head and he panicked. I could accept that and still not like it."
She continued, "I don't know how my nephews died. But the fact he could kill his own two children is beyond belief. That is something I'll never understand."