Crimean Tatars are a Muslim community indigenous to the Black Sea peninsula

Russian authorities in annexed Crimea raided the homes of Muslim Tatars Wednesday and detained at least 20 people suspected of belonging to a banned Islamist group ahead of this week's presidential vote in Ukraine.

Supporters decried the latest act of "intimidation" against members of the ethnic group, most of whom oppose Russia's annexation, and said the raids were among the largest in recent years.

Washington said it was "extremely concerned" by the arrests.

Most Crimean Tatars have refused to renounce their Ukrainian citizenship and some are planning to vote in the first round of Sunday's presidential poll.

In a statement, Russia's FSB security service said it had searched the homes of suspected members of the Hizb-ut-Tahrir group.

"Twenty of its rank-and-file members and leaders have been detained," the FSB said after conducting raids with police and other law enforcement agencies.

Hizb ut-Tahrir (Party of Liberation) seeks to re-establish a Caliphate -- a pan-Islamic state based on Islamic rule harking back to medieval times -- and has been banned in Russia since 2003.

The FSB accused members of the organisation of seeking to promote "an ideology based on terrorism" and recruit other Crimean Tatars. The security service claimed it had seized materials proving individuals' links to the banned group.

Lawyer Emil Kurbedinov said 23 people had been detained in large-scale raids that involved hundreds of FSB officers and other law enforcement agents.

"This is one of the largest acts of intimidation in Crimea in the last five years," Kurbedinov told AFP.

He said those detained included activists who fought for the rights of "Crimean political prisoners".

Another lawyer, Nikolai Polozov, said at least 25 homes across the peninsula had been raided, adding that defence attorneys were not allowed to oversee the searches.

Crimean Tatars are a Muslim community indigenous to the Black Sea peninsula.

Under Joseph Stalin's rule, they were sent into exile to Uzbekistan and the Urals and only returned around the fall of the USSR.

Most Crimean Tatars opposed Moscow's annexation of the peninsula in 2014 and subsequently Russian authorities have cracked down on the community, banning their assembly and television channel as well as detaining and jailing dozens of activists.

- 'Deportation into Russian jails' -

Nariman Jelyal, first deputy chairman of the Mejlis, the Tatars' banned assembly, linked the latest raids to the upcoming Ukrainian presidential elections, along with other factors.

He called the raids "the start of the mass deportation of the Crimean Tatars into Russian prisons".

"We are extremely concerned by Russia's raids and massive intimidation today targeting Crimean Tatars," the US embassy in Kiev said.

"We call on the Russian government to cease its unjust arrests, detentions, searches, and persecution of Crimean Tatars, activists, and journalists."

The Ukrainian foreign ministry denounced the arrests and called on the international community to ramp up its pressure on Russia.

"We don't rule out that today's events may become the start of a new wave of legal proceedings against the Crimean Tatars," the ministry said in a statement.

Amnesty International also condemned the raids.

"Russian authorities will resort to any means to suppress dissent, real or imaginary," Oksana Pokalchuk, head of the watchdog's Ukraine office said in a statement.

Crimean Tatars are a Muslim community indigenous to the Black Sea peninsula