The long-awaited homecoming of a marble fragment, honed to adorn the Parthenon but long in exile in Italy, must “open the way” for other masterpieces to be reunited with the monument, the Greek prime minister has said.

As the artwork was unveiled at the Acropolis Museum, Kyriakos Mitsotakis said its restitution – sealed in a breakthrough deal between Sicily and Athens – offered a blueprint for similar accords to be reached, for example with the UK.

“This important step today opens the way, I believe, for other museums to be able to move in a similar direction,” he told attenders at Monday’s ceremony. “Most importantly, of course, the British Museum should understand that the time has come for the Parthenon marbles … to finally return here, to their natural home.”

The exquisite piece is barely the size of a shoebox. Carved 2,500 years ago, it depicts the foot of a draped Artemis, goddess of the hunt, peeking out from beneath an elaborate tunic. The fragment once embellished the eastern part of the Parthenon temple’s monumental frieze, long regarded as the high point of classical art.

The treasure was returned last week to Greece by the Antonio Salinas Regional Archaeological Museum in Sicily, ostensibly as part of a cultural exchange.

Under the deal it was agreed that the loan, due to expire in 2026, could be extended for a further four years. In return, Athens has lent the Palermo Museum a headless fifth-century BC statue of the goddess Athena and an eighth-century BC amphora.

But culture ministry officials acknowledged negotiations were under way to ensure that the artefact’s repatriation was “indefinite”, in what would amount to added pressure on the British Museum to follow suit.

More than half of what survives of the 160-metre long frieze is on display in London. Lord Elgin, Britain’s then ambassador to the Sublime Porte, had the sculptures hacked from the monument more than 200 years ago before he sold them, bankrupt and despondent, to the British Museum in 1816.

Eight museums across Europe house other parts of the frieze; the Acropolis Museum in Athens, custom-built to exhibit the treasures, exhibits about 50 metres worth.

Mitsotakis, who has reinvigorated Greece’s decades-long campaign for the antiquities’ reunification in Athens, made the marbles’ restitution the central issue of his first Downing Street talks with the prime minister, Boris Johnson, in November.

Athens has long argued that the marbles were stolen by Elgin at a time when stateless Greece was under Ottoman rule.

Although once a passionate champion of the sculptures’ return to the country, Johnson has changed course, insisting that the carvings were legally acquired. He rejected Mitsotakis’ assertion that the row should be resolved as an intergovernmental matter, saying it was an issue for the British Museum to discuss.

But the Greek leader said on Monday that Athens remained undeterred in its battle to retrieve the treasures, and that the deal with the Palermo museum had proved that where there was a will, a “mutually acceptable solution” could be found. Athens has offered to give London antiquities that have never before left Greece in return for the masterpieces.

“I am especially encouraged by the fact that the majority of Britons appear to support our demand,” Mitsotakis said, referring to successive polls that have shown most UK citizens believe the marbles should be returned to Athens.