Sibneft, the Russian oil company, has shocked the financial markets by suspending its $19bn (€16bn) merger with larger rival Yukos. The deal was due to create the world's fourth largest oil producer.

Core shareholders in the two companies, agreed on Friday to put the deal on hold. The companies did not provide a reason for the decision and John Mann, a spokesman for Sibneft, declined to reveal whether talks have been suspended temporarily or permanently. The two held failed merger talks in 1998.