"That does suggest that the calculations are being made," said Kinninmont.

Less than 48 hours after he left the Saudi kingdom, five people were killed and 286 arrested on May 23 when police fired on a rally outside the home of Sheikh Isa Qassim, Bahrain's most high-profile Shiite cleric.

Trump last month embarked on his first foreign tour since taking office, beginning with Saudi Arabia where he had a string of meetings with Arab and Muslim leaders including Bahrain's King Hamad.

"The human rights situation was already bad, but the timing of the latest crackdown is striking and it's unlikely to be coincidental," said Jane Kinninmont, senior research fellow at Chatham House.

Authorities in Bahrain have clamped down on dissent in the wake of US President Donald Trump's visit to the Gulf last month -- a move that experts say is no coincidence.

Sign up for our Newsletter

"I think the main thing that is definitely different is... the amount of force that was just used. It does seem like a change."

Authorities said the sit-in, which had been going on for months, had become a refuge for "wanted persons

and fugitives".

On Wednesday, a state tribunal also dissolved the Waed movement, the country's main secular opposition group, on the grounds that it supported "terrorism".

The state last year ordered the dissolution of Shiite opposition group Al-Wefaq, once the largest bloc in Bahrain's parliament. Al-Wefaq leader Sheikh Ali Salman has been behind bars since 2014.

Sunni-ruled but Shiite-majority Bahrain has been rocked by unrest since 2011, when the authorities backed by a Saudi military force crushed Shiite-led protests demanding a constitutional monarchy and an elected prime minister.

The government accuses the mainly Shiite and Iran-backed opposition of "terrorism" aimed at toppling the state. Tehran has denied involvement.

'Blank cheque'

Gulf powerhouse Saudi Arabia worries about its regional rival Iran interfering in Arab states by using Shiite communities to advance Tehran's interests in Bahrain, Iraq, Lebanon and Yemen.

Trump has voiced similar concern, accusing the Islamic republic in his speech to Arab leaders in the Saudi capital Riyadh of exporting global "terrorism".

The American president, who ducked questions about human rights abuses during his Gulf visit, said ties with Manama would no longer be strained under his administration, unlike during that of his predecessor Barack Obama.

Bahrain, located between Saudi Arabia and Iran, is home to the US Navy's Fifth Fleet.

The US State Department is pursuing plans to sell F-16 warplanes to Bahrain, lifting restrictions put in place by Obama over the Al-Khalifa monarchy's crackdown on dissent.

Rights groups and analysts both warn that the worst is yet to come.

The London-based Bahrain Institute for Rights and Democracy said Trump "effectively gave Hamad a blank cheque to continue the repression of his people".

"Trump has effectively embraced longstanding US Gulf allies and, in a break from previous administrations, said that he would not lecture them on human rights issues

, signalling a hands-off US policy," said Adam Baron, visiting fellow at the European Council on Foreign Relations.

Hundreds of protesters have been arrested in Bahrain since 2011, including leaders of the opposition. Some including Qassim have also been stripped of their citizenship.

In April, the kingdom approved a constitutional amendment allowing military courts to try civilians accused of "terrorism", sparking condemnation by rights groups including Amnesty International and Human Rights Watch.

Last month, public prosecutors referred the first civilian case to a military court.