British police have arrested an 18-year old woman at a London airport on suspicion of preparing acts of terrorism and membership of a banned organisation, a police statement said.
Her arrest on Friday after she arrived on a flight at Stansted airport was connected to a prior investigation which had already resulted in the arrest of a 21-year-old man in October last year.
The woman was taken to a London police station where she remains in custody, the police said.
The arrest is the latest in a series carried out by British counter-terrorism officers since the country's threat level was raised in August to its second-highest level because of risks posed by Islamic State fighters returning from Iraq and Syria.
Much of Europe is currently on heightened security alert after last week's killings in Paris and raids in Belgium in which two gunmen were killed.
British Prime Minister David Cameron is in the United States for two days of talks with President Barack Obama where they have said they would tackle the threat posed by extremists.
