LONDON — The police in Britain said on Tuesday that they were investigating a claim that packages containing explosives sent to London and Scotland last week came from a group calling itself the I.R.A., an abbreviation for the Irish Republican Army.

The Metropolitan Police of London said in a statement that counterterrorism officers and the Scottish police were investigating the claim, including its indication that a fifth package was sent but remains undiscovered.

Four packages were found last week at the University of Glasgow and three London transport hubs, including Heathrow Airport. Employees near the airport opened one device, causing part of the envelope to burn, but no one was hurt. The other packages were recovered by the police before being opened.

“Given the packages received last week bore similarities to devices sent in the past which were linked to dissident groups associated with Northern Ireland-related terrorism, officers were already looking at this as a line of inquiry,” the police said. “However, we continue to keep an open mind.”