Canadian police announced on Monday that they had arrested two foreign men plotting to derail a passenger train and who had received some unspecified form of support from al-Qaeda personnel based in Iran.

The Royal Canadian Mounted Police said that Raed Jasser, a 35-year-old Palestinian living in Toronto, and Chiheb Esseghaier, a 30-year-old Tunisian living in Montreal, were arrested for conspiring to execute the first al-Qaeda-sponsored plot in Canada.

The two reportedly were planning to target a train travelling between Toronto and New York City. If this proves true, the plot would be the 55th foiled terrorist plot against the U.S. homeland since 9/11. American intelligence and law enforcement agencies, including the FBI, were involved in the investigation, according to The New York Times.

A Canadian police official said, “This is the first known al-Qaeda-planned attack that we’ve experienced in Canada.” Ahmed Ressam, the al-Qaeda-linked “Millennium Bomber,” formerly lived in Canada but was arrested for plotting to bomb the Los Angeles airport in 1999.

Officials stated that the plotters received “direction and guidance” from “al-Qaeda elements located in Iran,” but that there was no reason to think that the plot was state-sponsored (i.e., involved Iran’s government).

Iran’s radical regime long has had a murky relationship with al-Qaeda, which is inspired by a Sunni Islamist ideology that clashes with Iran’s radical Shia brand. But ideological differences were trumped by the fact that the two share common enemies: the United States, Israel, and moderate Arab governments.

According to the 9/11 Commission Report (page 61) Iran long has cooperated with al-Qaeda:

In late 1991 or 1992, discussions in Sudan between al Qaeda and Iranian operatives led to an informal agreement to cooperate in providing support—even if only training—for actions carried out primarily against Israel and the United States. Not long afterward, senior al Qaeda operatives and trainers traveled to Iran to receive training in explosives. In the fall of 1993, another such delegation went to the Bekaa Valley in Lebanon for further training in explosives as well as in intelligence and security. Bin Ladin reportedly showed particular interest in learning how to use truck bombs such as the one that had killed 241 U.S. Marines in Lebanon in 1983.The relationship between al Qaeda and Iran demonstrated that Sunni-Shia divisions did not necessarily pose an insurmountable barrier to cooperation in terrorist operations.

The 9/11 Commission Report (page 241) concluded that although Iran had facilitated the travel of al-Qaeda members in and out of Afghanistan, including at least eight of the 9/11 hijackers, it found no evidence that Iran was aware of the planning for the 9/11 attacks. The 9/11 Commission Report also concluded, however, that “[w]e believe this topic requires further investigation by the U.S. government.”

After the U.S. overthrow of the Taliban, which provided al-Qaeda sanctuary in Afghanistan, Iran offered refuge to the terrorists and facilitated their travel between Afghanistan and Iraq. CNN’s Peter Bergen reported that the Pentagon made plans in 2002 to raid an al-Qaeda safe house in the Iranian town of Chalus, but the raid was called off due a lack of precise intelligence.

U.S. intelligence agencies concluded that a May 2003 terrorist bombing in Saudi Arabia was planned and ordered by al-Qaeda elements located in Iran, according to The Washington Post. Senior al-Qaeda leaders, including Osama bin Laden’s son, Saad, and al-Qaeda’s military commander Saif al-Adel, lived in Iran for many years under the protection of the elite Quds Force of the Islamic Revolutionary Guard Corps.

Although Tehran periodically restricted its activities under some form of house arrest, it relaxed its grip and allowed many al-Qaeda cadres to leave Iran beginning in late 2008.

An anonymous U.S. government source suggested that the Canadian train plot may be tied to a network of al-Qaeda facilitators based in the city of Zahedan, near Iran’s borders with Afghanistan and Pakistan.

Iranian Foreign Minister Ali Akbar Salehi publicly dismissed a link between al-Qaeda and Iran as “ridiculous,” and claimed that “[t]his is the most hilarious thing I’ve heard in my 64 years.”

But the Canadian plot and Iran’s long-standing links to terrorism are no laughing matter. Iran may not be calling the shots for al-Qaeda, but it is at a minimum enabling and turning a blind eye to al-Qaeda’s murderous activities.