Police have arrested a fourth man allegedly involved in an Ottawa terrorist cell, part of a bombing and terror financing plot that experts say stretched from Canada to the Middle East and war-torn Afghanistan.

Security consultant Michel Juneau-Katsuya, a former CSIS officer, told CTV News Channel that authorities are searching for at least three more men in the plot, which sources have told him would have targeted the Parliament buildings and Montreal's public transit system with bombs.

"We know that the ringleader went to Afghanistan and to Pakistan to receive some training, so right there there's a certain international connection," he said.

"We have been told also that some of their suspected accomplices could be in Iran or in Dubai."

Juneau-Katsuya said the accused were assembling components for one or more bombs and had raised money for al Qaeda and the Taliban, currently fighting Canadian and NATO troops in southern Afghanistan.

"We knew that the ringleader was about to take a trip abroad, maybe to deliver the money himself," he said.

Khurram Syed Sher, 28, of London, Ont., appeared in court Friday on charges of conspiracy to facilitate terrorist activity

The McGill University graduate, who worked as an anatomical pathologist at St. Thomas Elgin General Hospital in St. Thomas, Ont., just south of London, was arrested with two other men after a year-long investigation and a search which police say uncovered more than 50 circuit boards designed to remotely detonate bombs.

The bearded father of three and avid hockey player appeared nervous during the brief court appearance, where a justice of the peace ordered him to return Sept. 1 via video feed.

The others charged are Hiva Mohammad Alizadeh, 30, and Misbahuddin Ahmed, 26, both of Ottawa. They both appeared in court on Thursday. Like Sher, they are also Canadian citizens.

Ahmed faces the same charge as Sher -- conspiracy to facilitate terrorist activity.

But Alizadeh is charged with conspiracy, committing an act for terrorism purposes and providing or making available property for terrorism purposes.

He is also charged with making or having "an explosive substance" with the intent to endanger life or cause serious damage to property. Police said the circuit boards are considered an explosive substance under the Criminal Code.

An Iranian man has told a Canadian newspaper that there is no substance to allegations that he and his brother are part of an alleged terror cell that sought to attack targets in Canada.

Speaking through a translator, Rizgar Alizadeh told the Globe and Mail in a telephone interview that he has never travelled outside Iran and denied any suggestion that he or his brother are connected to terror groups.

He called the allegations made by Canadian authorities "a pack of lies."

But court documents allege they conspired with "James Lara, Rizgar Alizadeh and

Zakaria Mamosta, and person or persons unknown" in their activities.

The Mounties described the three as members of a home-grown terrorist group, although they said Alizadeh is a member of another group with links to the Afghan war.

Juneau-Katsuya said Canadian authorities face an uphill struggle in tracking down some of the alleged members of the conspiracy who are living abroad.

"This is already quite a challenge, dealing with (police) organizations in different countries … the countries you are dealing with are not necessarily friendly or are suspicious to say the least," he said.

"The problem that we have for example in Pakistan (is that) the secret services are suspected to have quite a lot of sympathizers to the Taliban and to al Qaeda."

Terrorism expert Alan Bell expects that authorities may announce further arrests as the investigation into the Ottawa group continues, though they may not come immediately, such as in the case of the Toronto 18.

"You have to remember, it took the Toronto 18 court case…three to four years before it came to fruition," Bell told CTV News Channel during an interview in Toronto on Saturday morning. "

"This is more complicated, it's got international connections, which the Toronto 18 case didn't have. So all those things are going to be taken into consideration."

Police say a terror attack was likely still months away when they pounced on the plot, but they moved because they feared the men were about to start sending money to other terrorists in Afghanistan.

Juneau-Katsuya said the alleged plotters apparently used public computers in Ottawa libraries to share information -- in an attempt to avoid police surveillance.

"In the game of counter terrorism, the terrorists have the upper hand. They can hide within the community, they can disappear very quickly in some cases … unfortunately despite all the money that we spend and despite the success … if one guy gets through the net it makes a mockery of all the good work that's been done."

With files from The Canadian Press