Counter-terror police are still working to identify a motive or suspect over the explosive packages sent to major transport hubs as sorting offices are on high alert for further devices.
Deputy Assistant Commissioner Dean Haydon, the senior national co-ordinator for counter-terrorism policing, said on Wednesday that no link had been made with Irish dissidents at this stage.
The packages that arrived at Waterloo railway station and offices at Heathrow and London City Airports on Tuesday were posted with Irish stamps and had Dublin as the return address, prompting Irish police to join the investigation.
But Mr Haydon said no message appeared to be contained within the packages, no sender had been identified, and no group had claimed responsibility.
“We are talking to our Irish counterparts but at the moment there’s nothing to indicate motivation of the sender or ideology, so I cannot confirm at the moment if it’s connected to any Ireland-related terrorist groups,” he said.
Asked whether there could be more packages, he replied: “They were sent through the postal system so we are not ruling that out.
“We’ve only seen three but, as a result, we’ve sent our detective security messaging across the country to key places and locations that have sorting offices with a view to identify if there are more and then hopefully we can intercept them at an early stage.
“But there’s no indication there’s any more.”