The massacre of 38 tourists on a Tunisian beach is being linked to an earlier attack in the country that killed 22 people.

The victims of both attacks - in Sousse and the Bardo Museum in Tunis - were mostly western tourists.

Three Irish people were among those killed in the June attack.

Britain's Metropolitan Police Commander Richard Walton said the connection was based on "strong" evidence but did not provide further details.

"We are now linking evidentially the Bardo Museum investigation with the Sousse investigation," he said.

Tunisian authorities have arrested 150 people in relation to the Sousse attack and 15 have been charged with terrorism offences.

Gunman Seifeddine Rezgui opened fire on sunbathing tourists on the beach and a hotel in June before he was shot dead by police.

Tunisian authorities say he acted alone during the attack, but had accomplices who supported him beforehand, providing him with weapons and logistical support.

Scotland Yard say detectives investigating the Sousee massacre have spoken to 459 witnesses and some believe they saw a second gunman wearing red shorts.

However it is now thought this suspect was a hotel security worker who attempted to tackle Rezgui.

Some 370 items of photographic evidence are also being examined by detectives.

One of the country's top security officials has confirmed Rezgui was trained in neighbouring Libya at the same time as the attackers who targeted the Bardo Museum in March.

Terrorist group Islamic State later released an online audio recording in which it claimed responsibility for the massacre.

Security forces in the country have remained on high alert since the attacks.