Yo-Yo Ma, one of the world's greatest cellists, warned US congressmen yesterday that visa restrictions introduced after the September 11 attacks had reduced the number of foreign artists performing in the US.

Mr Ma, a US citizen born in France of Chinese parents, told the House government reform committee that "it has become increasingly difficult to facilitate cultural exchange because of the high financial cost, uncertain timeline and countless logistical hurdles" involved in getting US visas.