LONDON (Reuters) - British singer Sting has cancelled a concert in the Kazakh capital Astana scheduled for Monday after human rights group Amnesty International informed the former Police frontman about what it described as a crackdown on oil workers there. Several thousand workers at UzenMunaiGas, a unit of London-listed oil producer KazMunaiGas Exploration Production, went on strike on May 26, saying their salaries had been cut and their lawyer imprisoned on false charges. The company has called the strike illegal and a spokesman said last week that around 250 employees had been fired for breaching their contract terms. Sting, criticised for performing in 2009 in Uzbekistan which is widely regarded as one of the most repressive countries to emerge from the Soviet Union, described the treatment of the Kazakh workers as unacceptable. Hunger strikes, imprisoned workers and tens of thousands on strike represents a virtual picket line which I have no intention of crossing, the 59-year-old said in a statement. The Kazakh gas and oil workers and their families need our support and the spotlight of the international media.