Rail travelers between Britain and France have been warned of delays up to three hours after a large group of migrants get on to tracks overnight in the French port city of Calais.

Eurotunnel said a "highly organized group of more than 100 migrants" broke into the tunnel terminal in Calais at about 22:30 GMT Friday. All services were suspended overnight "for safety reasons".

Eurostar and vehicle ferry service have resumed progressively Saturday.

The French police took control of the situation on site to prevent migrants crossing to the U.K., according to Eurotunnel.

"Such a large group had no chance of reaching the U.K., so this was clearly an organized attack aimed at drawing media attention to the desperate situation of the migrants who are stuck in Calais", Eurotunnel said in a statement.

Two police officers and four migrants suffered minor injuries, local authorities of the Pas-de-Calais region said.

Calais is a focal point for thousands of migrants who are trying to cross illegally from France into Britain.

Security surrounding the tunnel beneath the English Channel has been ramped up in recent months. Barbed wire fences are going up around the complex, which has a perimeter of 28 kilometers (17 miles), and security teams have been bolstered with more police and dogs at the site.

On Wednesday, an Eritrean migrant was found dead in the tunnel, the latest of 13 migrants killed this year in the area, most of them on the Eurotunnel site. The administration for the Pas-de-Calais region says the migrant was apparently hit by a freight train near the entrance to the tunnel in Calais.