Four people have been charged with carrying out a terrorism-related prank in relation to smoke-bomb attacks that shut down the Montreal subway system for hours, reports indicate.

The suspects, a man and three women, were also charged with conspiracy and mischief of over $5,000 for Thursday's prank, the Canadian Press reports. As well, the 22-year-old man was charged with possession of a prohibited weapon.

Officers say the suspects, in their early twenties, turned themselves in to police. The group appeared in a video conference arraignment on Saturday. They faced charges of inciting fear of terrorism, which is punishable by a maximum five-year prison sentence.

According to CP, the four will appear in court on Monday.

The smoke-bomb attacks were carried out in different areas of the city's subway system and shut down the metro for hours during the peak period, creating havoc for Montreal commuters.

Eyewitness photos of the suspects circulated in newspapers and on the Internet.

It is estimated that the subway closure cost the city several million dollars in lost productivity.

Unconfirmed reports suggest the attacks could be linked to a group of militant student protesters who have been protesting the government's proposed tuition increases. Reports say the group feels that the main student protesters are not far-reaching enough in their demands.

As Montreal's festival season approaches, there are concerns that the protests may disrupt the city's famous Formula One Grand Prix parties, as well as the comedy and jazz festival.

A group of students from the Université du Québec à Montréal this week criticized the protests for being too peaceful and promised to disrupt the Grand Prix parties in June.