MOSCOW (REUTERS) - Former Soviet leader Mikhail Gorbachev urged the presidents of Russia and the United States on Thursday to help broker negotiations to end violent protests in Ukraine, which he said was facing a possible "catastrophe".

At least three people died in the latest clashes this week between anti-government protesters and riot police in Kiev. On Thursday, President Viktor Yanukovich called for an emergency session of parliament to discuss the crisis.

Mr Gorbachev, 82, a Nobel Peace laureate whose reforms helped end the Cold War but led to the Soviet Union's demise, appealed to Russia's President Vladimir Putin and US President Barack Obama to help Ukraine resolve the conflict peacefully.

"Without the help, without the cooperation of authoritative representatives of our two countries this (situation) could lead to catastrophe," Mr Gorbachev, who has Ukrainian heritage, said in an open letter posted on his foundation's website.

"I ask you to seize the opportunity and take a decisive step to help Ukraine return to the path of peaceful development. I am really relying on you," he said. "The opposing sides should sit at the negotiation table." His call for further talks in Ukraine echoed the view of current leaders such as German Chancellor Angela Merkel, who expressed outrage on Thursday over Ukraine's crackdown on the protesters and said the focus must be on de-escalation and dialogue.

The protests erupted in November after Mr Yanukovich rejected a trade pact with the European Union in favour of boosting ties with Russia, Ukraine's Soviet-era master.

Mr Gorbachev, who was born into a mixed Russian-Ukrainian family in 1931, is disliked by many Russians for what they see as his role in the collapse of the Soviet Union in 1991, which was followed by years of political and economic chaos.