The event would have marked the first time that HRW representatives had been able to enter the Persian Gulf state since 2012, according to Reuters.
Bahrain, a U.S. ally, will from Saturday host the 146th assembly of the Inter-Parliamentary Union (IPU), an international organisation with the motto “For democracy. For everyone”.
HRW, which has permanent observer status with the IPU and was granted the visas earlier this year, had on Monday called for conference attendees to raise concerns about what it called “the serious repression of human rights in Bahrain”.
The IPU said it was aware the visas had been revoked by Bahraini authorities. A spokesperson said the IPU did not know of any other delegations that had had restrictions imposed on them to attend the meeting.
Bahrain’s government communications office did not immediately respond to a request for comment.
Rights groups, including HRW, have criticised Bahrain for holding international events, such as last week’s annual Formula One race, as a way of distracting from repression of political opposition. The country has, since a 2011 anti-government uprising, jailed thousands of people, including opposition leaders, sometimes in mass trials. It has also dissolved leading opposition groups.
Bahrain’s government says it has made key reforms in recent years on human rights, criminal justice and prisoner treatment.