(CNN) -- The Royal Canadian Mounted Police said authorities Friday took a fourth person into custody in their ongoing investigation into domestic terrorism.
The RCMP said its Integrated National Security Enforcement Team executed a search warrant in Ottawa and took one person into custody. No charges have been filed.
Earlier Friday, a Canadian government source close to the investigation said the three men arrested previously "are not card-carrying members of al Qaeda but they follow in the movement and show common trends."
RCMP Chief Superintendent Serge Therriault said Thursday the three suspects are Canadian citizens living in Ontario -- Hiva Mohammad Alizadeh, 30, of Ottawa; Misbahuddin Ahmed, 26, of Ottawa; and Khurram Syed Sher, 28, of London.
The name of the suspect arrested Friday has not been released.
Alizadeh faces three charges: conspiracy, committing an act for a terrorist group and providing or making available property for terrorist purposes. Canadian federal prosecutor David McKercher told CNN the three charges carry maximum sentences ranging from ten years to life in prison.
Ahmed has been charged with conspiracy, but he could face more charges, according to his defense attorney. Ian Carter told CNN he met with Ahmed for half an hour. Asked how the suspect was feeling, Carter said, "He is in shock." Ahmed is married and has a 7-month-old daughter.
Sher also is charged with conspiracy, officials said.
The RCMP said the three suspects were arrested under Canada's Anti-Terrorism Act, passed in 2001.
Therriault said that a yearlong investigation found that in addition to forming part of a terror cell, the suspects possessed schematics, videos, drawings, instructions, books and electrical components designed specifically for the construction of improvised explosive devices. He said authorities seized more than 50 circuit boards designed to remotely detonate IEDs.
In addition, Therriault said, investigators have grounds to believe Alizadeh is a member of and remains in contact with a terror group with links to the conflict in Afghanistan. One reason the arrests happened when they did, the investigator said, was to prevent Alizadeh from providing financial support for weapons that would be used against coalition forces and Canadian troops in Afghanistan.
The three suspects represent the core of the domestic terror group, Therriault said, but the ongoing investigation could result in more arrests.
There are no related arrests in the United States, a federal law enforcement official told CNN.
The official said there is no clear link between the Canadian suspects and the United States. Therriault said he could not confirm whether there was a direct link to the United States.
A Canadian government source close to the investigation told CNN the United States is not the focus of the investigation.
U.S. counterterrorism officials said they consider the arrests an internal Canadian matter.
CNN's Laura Dolan contributed to this story.