"As I understand it, it was a train going from Canada to the U.S.," Rep. Peter King, R-New York, chairman of the counterterrorism and intelligence subcommittee, told CNN.

While the Royal Canadian Mounted Police officials who announced the arrests refused to discuss which train route was targeted, other U.S. government sources said the plot involved a Toronto-New York train that is operated by the Canadian Via Rail system and Amtrak.

The train crosses the U.S.-Canadian border at the Whirlpool Bridge, a two-level bridge that has vehicle traffic on the lower level and a railroad track on the top north of the Rainbow Bridge.

Canadian officials acknowledged that the threat targeting a Via Rail train route was gravely serious.

"Had this plot been carried out, it would have resulted in innocent people being killed or seriously injured," James Malizia, the assistant commissioner of the Mounties, said at a Toronto press conference.

While the perpetrators had the "capacity and intent" to carry out the attack, rail passengers and the rail system were not under imminent danger, Malizia added.

Arrested in the plot were Raed Jaser, 35, of Toronto, and Chiheb Esseghaier, 30, of Montreal. Canadian authorities offered few details about the two men, other than saying they were not Canadian citizens.

Jaser and Esseghaier are charged with conspiring to carry out an attack against, and conspiring to murder persons unknown for the benefit of, at the direction of, or in association with a terrorist group. They are scheduled to make their first court appearance in Toronto on Tuesday.

While details of the alleged plot remained sketchy, officials did reveal some shocking details.

"This is the first known al-Qaeda planned attack that we've experienced in Canada," said Doug Best, superintendent of the Mounties, at a separate news conference.

What's more, Malizia said, "the individuals were receiving support from al-Qaeda elements located in Iran."

That aid consisted of "direction and guidance" from those elements, said Jennifer Strachan, chief superintendent of the Mounties.

"There is no evidence to indicate that these attacks were state-sponsored," she added.

While al-Qaeda is believed to have a stronger presence in some Arab countries as well as Southeast Asia, Rep. Brian Higgins, D-Buffalo, said it's no surprise that Canada-based terrorists would receive help from elements of the terror group based in Iran.

While Iran is noted for a stronger presence of Hezbollah, another terror group, "these groups are linked in some way shape or form," said Higgins, the top Democrat on the Counterterrorism and Intelligence Subcommittee. "Terrorists are terrorists. They're like-minded in organization and approach."

Higgins has, for years, warned of Hezbollah's Toronto presence, saying it may not be connected only to the financing of terror attacks, as Canadian officials have indicated.

"We have to always be vigilant, but we also need to remain calm" in the wake of the reported plot to attack the Toronto-New York train, Higgins added. "The disclosure of this plot is a good thing. It means we are catching a terrorist attack before it occurs."

In the course of the investigation, authorities found that the two men were staking out their potential targets.

"They watched trains and railways in the Toronto area," Strachan said.

The RCMP officials said they initiated the investigation last August and worked with regional law enforcement as well as the FBI and railroad officials.

Amtrak's president and CEO, Joe Boardman, issued a statement saying he "appreciates the actions" of the Mounties.

"The Amtrak Police Department will continue to work with Canadian authorities to assist in their efforts and refers all inquiries about the investigation to the RCMP," Boardman said. "There was not an imminent threat to Amtrak passengers, employees or the general public."

Meanwhile, David C. Jacobson, the U.S. ambassador to Canada, highlighted the cross-border investigative work involved in the case.

"It underscores the fact that we face serious and real threats, and that security is a shared responsibility," Jacobson said. "We all need to remain vigilant in confronting threats and keeping North America safe and secure."

Sen. Charles E. Schumer, D-N.Y., agreed.

"New York shares a common border and common threat with our partners to the north and I salute the Canadian law enforcement, the FBI, and the US Department of Homeland Security for working together on a job exceedingly well-done," Schumer said.

News Albany bureau chief Tom Precious contributed to this report.