There are “strong” links between last June’s Tunisia beach massacre and the killings at the Bardo Museum in the country’s capital in March, British police say.
Metropolitan Police counter-terrorism officers say they are now connecting the two attacks based on evidence.
The Bardo Museum attack saw 22 people killed, while 38 tourists, including 30 British nationals, were killed in the resort of Sousse in June.
The militant group Islamic State (IS), has said they were behind both attacks.
Tunisian authorities have arrested 150 people to date, over the Sousse attack.
Of those, 15 have been charged with terrorism offences.
Those charged face allegations including being involved in a terrorist plot, not informing police of a plan and providing logistical or other support.
A trial in relation to the murders is not expected to take place for up to 18 months.
Commander Richard Walton, of the Metropolitan Police, which supplied officers to help the Tunisian investigation into the massacre, gave no details of the suspected connection between the attacks but said it was based on “strong” evidence.
Tunisian authorities have also drawn a connection between the attacks, saying that the Sousse attacker likely trained at the same Libyan jihadi camp as the two Bardo attackers.
In Sousse a gunman, who was later identified as Tunisian student Seifeddine Rezgui, opened fire on the beach after coming in from the sea using a jet ski or speedboat.
After shooting on the beach, he entered the Hotel Imperial Marhaba, where explosives were detonated and more tourists were shot. Rezgui then ran out of the hotel and police shot him dead.
Tunisian authorities believe the 23-year-old’s suspected accomplices provided a Kalashnikov assault rifle and helped Rezgui get to the scene, interior ministry spokesman Mohamed Ali Aroui told AP.