Greek police have detained 10 foreign activists suspected of helping migrants enter the country from neighbouring Turkey, a spokesman said Tuesday.

A probe over several months on the islands of Lesbos, Chios and Samos, all close to Turkish shores, led to the detentions, the northern Aegean police told AFP.

Of them, four belonged to different humanitarian groups suspected of "having facilitated the entry into the country" of migrants from Turkey, police spokesman Nikos Ververis told AFP.

They included a Norwegian, British and US citizen belonging to three different NGOs, as well as two Syrians and four Afghans, he said.

Ververis could not specify the nationality of the 10th suspect.

Eleftherios Douroudous, head of the northern Aegean police, said the operation, which kicked off in June 2020, targeted "illegal migration networks".

Police said the suspects created social media accounts and used migrants' information in support of their activism.

The European Union and the UN refugee agency UNHCR have repeatedly called on Greece to review allegations of turning back migrants from Turkey.

UNHCR has recorded around 300 incidents of alleged illegal expulsions around the Aegean islands and the land border between Greece and Turkey between January 2020 and March 2021.

But the conservative government in power since mid-2019 has consistently denied the allegations, insisting that arrivals have decreased significantly.