Scotland Yard counter-terrorism officials have established "strong" links between June's Tunisia beach massacre and the killings at the Bardo Museum in the country's capital in March.
Metropolitan Police officers, who have been helping Tunisian authorities in their investigations, say they are now connecting the two attacks based on evidence, the BBC reported.
The Bardo Museum attack resulted in 22 deaths, while 38 tourists, including 30 British nationals, were killed in the beach resort of Sousse in June.
Tunisian authorities have arrested 150 people to date over the Sousse attack and 15 have been charged with terrorism offences.
Commander Richard Walton, of the Metropolitan Police which supplied officers to help the Tunisian investigation into the massacre, said he would not provide more details of the suspected connection but stated it was based on "strong" evidence.
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 and shot more tourists there before running out of the front of the hotel where police shot him dead.
The militant group Islamic State (IS) later said it was behind the attack. The Bardo Museum in Tunis was stormed by three gunmen on March 18. British, Japanese, French, Italian and Colombian tourists were among the 22 killed.
Two of the gunmen, identified by the authorities as Yassine Laabidi and Hatem Khachnaoui, were killed by security forces. IS had claimed responsibility for that attack as well.
