A 19-year-old man arrested at Heathrow airport on suspicion of "Syria related" terrorism offences has been released on bail, the Metropolitan Police have said.
Officers have since completed the search of an address in the Camden area of north London.
In a statement, the police said the arrest is "not in response to any immediate risk or threat".
A second man also arrested at the airport on Saturday on suspicion of assisting terrorism in Syria is still being held in custody.
A 20-year-old British man has been arrested at Heathrow airport on suspicion of assisting terrorism in Syria.
The Briton is the second man to be arrested at the busy airport on suspicion of terror offences today.
Earlier, a 19 year-old was held on suspicion of preparing for acts of terrorism in what police described as a "Syria-related" incident.
Police said the two arrests are not connected. Both men remain in custody in London.
The terror-related arrest of a teenager at Heathrow airport was not made in response to any immediate risk or threat, police said.
A 19-year old man has been arrested on suspicion of "preparing for acts of terrorism" in relation to Syria.
The man is currently held at a police station in London.
A 19-year old man has been arrested at Heathrow airport on suspicion of "preparing for acts of terrorism" in relation to Syria, police said.
The man is being held at a police station in London and an address in the north of the city is being searched, the Metropolitan police said in a statement.
The government-appointed Commission into airport expansion has revealed its shortlist of preferred options. It lists a third runway at Heathrow and a second at Gatwick in Sussex.
The Commission, chaired by former FSA chief Sir Howard Davies stopped short of listing Stansted for possible expansion.
The Commission's preliminary report said only one extra runway would be needed in the south east before 2030 with an additional runway likely to be needed by 2050.
Plans for a hub in the Thames Estuary - dubbed "Boris Island" were not shortlisted because of "too many uncertainties and challenges".
It said it would undertake further study of the Isle of Grain option in the first half of 2014 and "will reach a view later next year on whether that option offers a credible proposal for consideration alongside the other shortlisted options".
British Airways has tweeted that fog is causing delays and some cancellations at Heathrow Airport.
Heathrow Airport reports that the M25 spur connecting Terminal 5 to the M25 has been temporarily closed. This is in an outbound direction heading away from the terminal.
US officials investigating the fire on a Boeing 787 Dreamliner jet at Heathrow airport last week are focused on how condensation in the plane and a possible pinched wire in an emergency beacon may have sparked the blaze, Reuters reported, citing an unnamed source.
The US Federal Aviation Administration (FAA) said it will call for inspections of the beacons made by the Fortune 100 firm Honeywell, but stopped short of requiring airlines to disable or remove the devices as the UK's Air Accidents Investigation Branch recommended.
The FAA said inspections should ensure wires are properly routed and should look for pinched wires or signs of unusual moisture or heat. It gave no further details on how those factors may have contributed to the fire.
But a source told Reuters that investigators had found a pinched wire in the casing of the emergency locator transmitter (ELT) on board the Ethiopian Airlines flight.
Airports across the UK are advising passengers to check whether their flight has been cancelled with their airline before travelling and to allow extra travel time.