LONDON - London police have arrested four suspected Islamic terrorists in several raids throughout the British capital.

Police said Tuesday that officers fired a stun gun at one 21-year-old suspect, but he did not need medical treatment. The four suspects are aged 20 and 21.

Police say they were arrested on suspicion of preparing or instigating acts of terrorism.

Armed police from a specialist unit took part in one of the raids, indicating that the situation was deemed potentially dangerous to officers.

Police said no shots were fired when the search warrant was executed.

The suspects remain in custody, and homes and vehicles in west and central London are being searched as part of what police called an ongoing investigation into Islamic-related terrorism.

The terror threat in the U.K. was recently raised to ``severe'' because of the increase in the number of Britons traveling to Syria to join up with the Islamic State group.

The government has said the militant group plans to strike targets inside Britain.