British authorities say they are stepping up security at events marking Armed Forces Day across the country amid a news report that officials foiled a bomb attack by the Islamic State group on a military parade in London.

The announcement follows attacks in Tunisia, France and Kuwait on Friday.

The Sun newspaper said police foiled an attack on a London parade Saturday after an undercover reporter who obtained details on the plot alerted counter-terrorism officials.

Prime Minister David Cameron told reporters there will be "heightened security" at events paying tribute to Britain's military. He did not elaborate.

Police said security is also being beefed up for the annual gay pride parade in London Saturday.

Britain's terrorism threat remains at "severe," the second-highest level, meaning an attack is considered highly likely.