LONDON (AFP) - British police said on Thursday that they had arrested two more people over alleged involvement in terrorism in Syria following the discovery of ammunition at the port of Dover.

A man aged 27 and a woman aged 26 were detained at a house in Essex, east of London, on Wednesday following a search and are still being questioned, the Metropolitan Police said.

They were held "on suspicion of being involved in the commission, preparation and instigation of acts of terrorism", it said.

Their arrests came after two men aged 29 and 22, both British citizens, were held on Monday in Dover in southern England after arriving from Calais in France. A quantity of ammunition was seized.

"The arrests relate to suspected terrorism in Syria," the police said.

Police were carrying out searches at premises in London and in Lancashire, northern England.

British police have in recent months arrested a number of people on suspicion of travelling to Syria to fight with Islamist rebel groups opposed to President Bashar al-Assad.