Armed police officers are patrolling some bus and railway stations across Wales as part of a UK-wide operation.
Police at Cardiff Central after the 7 July London bombings
Their presence on Thursday coincides with a precautionary high alert across the UK's transport system.
British Transport Police said efforts to reassure the public and deter would-be attackers had seen the rail system's "largest ever deployment".
A South Wales Police spokesman said there was no increased risk but it was hoped it would offer added reassurance.
However, Metropolitan Police Commissioner Sir Ian Blair warned it was possible "that those at large will strike again," or that another cell could do so.
As well as public transport stations, armed officers are also patrolling at locations such as Sarn motorway services on the M4 near Bridgend.
Armed officers are patrolling platforms at Cardiff Central
In north Wales, armed officers are at the main port of Holyhead and there are also patrols at a number train and bus stations and "other potentially vulnerable sites".
Checks along the main arterial routes within North Wales will also continue.
South Wales Assistant Chief Constable Dave Francis said: "The presence of armed police officers at railway stations and other public places in south Wales today is to provide reassurance to local people, visitors and commuters.
"South Wales Police is here to protect the public and it is our priority to ensure everyone feels safe. This high visibility policing is intended to provide added reassurance.
"There is no specific threat or intelligence to indicate that Wales may be a target for terrorist activity, or that there is any link between those responsible for the London terrorist attack.
"But South Wales Police must keep an open mind, and everyone is being urged to remain vigilant, alert but not alarmed.
"But we are determined that it will be very much business as usual, keeping Wales safe and enabling people to go about their daily lives."