Counter terror police working to identify a motive or suspect over the three improvised explosive devices found on Tuesday.
The packages were sent to three major transport hubs, and the sorting offices are now on high alert for any further devices.
Dean Haydon, the deputy assistant commissioner, the senior national co-ordinator for counter-terrorism policing said on Wednesday despite Irish stamps on the envelopes, no link has been made with Irish dissidents.
Haydon further said no sender had been identified, and no group had claimed responsibility and no message appeared in any of the packages,
Hayden said, “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
Hayden was asked could there be more packages he said, “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.”
On Wednesday three explosive packages were sent to London City Airport, Waterloo Station and London Heathrow Airport. Due to the envelops having Irish stamps on them, this has prompted Irish police to investigate.