German authorities said on Monday they detained another person in relation to a suspected terror plot on the world-famous Cologne Cathedral, bringing the total number of arrests to five.

The suspect was a 41-year-old German-Turkish man who was arrested on Bochum on Sunday night.

Earlier, on Sunday morning, police detained three others who were later released. Police also detained a 30-year-old Tajik national on Christmas Eve.

On Monday, police extended the detention of two suspects so that they could be held for up to 14 more days for questioning.

All of the suspects are allegedly affiliated with IS-Khorasan, an offshoot of the so-called "Islamic State" group in Afghanistan.

Cologne Cathedral under guard

Local media reported that the suspected terror plot was supposed to have been carried out on New Year's Eve with a car loaded with explosives.

On Sunday, Cologne police said that the cathedral's underground parking garage had been searched and that explosives detection dogs had been deployed, but nothing was found.

On Monday, police said they would continue guarding Cologne Cathedral.

"How long this measure will be maintained is currently under review," a police spokesperson said.

zc/kb (dpa, AP, AFP)