Oscar-winning actor Hilary Swank and action star Jean-Claude van Damme have been criticised for attending a lavish party in honour of Chechen president Ramzan Kadyrov. Human rights organisations targeted the pair for agreeing to be part of the multimillion-pound event on a floating stage on the river Sunzha in the Chechen capital city, Grozny, last Wednesday.

In 2009, the American organisation Freedom House named Chechnya alongside Burma, North Korea and Chinese Tibet on a list of the most repressive societies in the world.

"Ramzan Kadyrov is linked to a litany of horrific human rights abuses," said a statement from Human Rights Watch (HRW). "It's inappropriate for stars to get paid to party with him. It bolsters his image and legitimises a brutal leader and his regime. And getting paid to be part of such a lavish show in Chechnya trivialises the suffering of countless victims of human rights abuses there."

According to the Hollywood Reporter, Swank and Van Damme were probably paid six-figure sums to attend the event. The action star went on stage and told his host: "I love you, Mr Kadyrov", while Swank wished the leader a happy birthday and said she was honoured to be in the Chechen capital. The British violinist Vanessa Mae also performed for what local media said was a fee of half a million dollars (£320,000).

Swank came in for particular criticism because her manager had earlier told the Human Rights Foundation (HRF) she had no plans to attend the ceremony. Representatives for both figures have remained silent on the matter. Actors Eva Mendes and Kevin Costner declined invites to attend the event.

• This article was amended on 12 October 2011 to correct the abbreviation of Human Rights Watch to HRW from HRF, and to clarify that HRF stands for the Human Rights Foundation.