A dozen men suspected of plotting terrorism were arrested Monday, British law enforcement officials said. 

The arrests came after British police conducted early morning raids in three cities. Assistant Commissioner John Yates, the U.K. 's lead police officer for counterterrorism, said the suspects were detained in London, in the central English city of Stoke-on-Trent and in Cardiff, Wales.

The 12 suspects are being questioned on suspicion of preparing acts of terrorism, but police have not disclosed the details of the alleged plot.

"The operation is in its early stages so we are unable to go into detail at this time about the suspected offenses," Yates said in a statement. "However, I believe it was necessary at this time to take action in order to ensure public safety."

Officers said the suspects range in age from 17 to 28 years old. They will be questioned on suspicion of commissioning, preparing, or instigating acts of terrorism.

Yates said the latest arrests followed close coordination by officers from several different cities.

"This is a large scale, pre-planned and intelligence-led operation involving several forces," he said.