"Deutsche Boerse shares have been suspended since 1521 GMT," the spokesman said.

He was not able to say why the stock had been halted but the move came amid rumours the market operator was mulling a tie-up with NYSE Euronext, which also saw trading of its shares suspended in Paris and New York.

"We are going to release a statement today but we have no other comment for now," NYSE Euronext told AFP.

Earlier in the day, the London and Toronto stock exchanges unveiled a landmark merger to create one of the world's biggest trading platforms that will dominate the raw materials and energy sectors.

The transatlantic tie-up will be positioned to take advantage of growing global demand for commodities and will be well placed to fend off stiffer competition.

Deutsche Boerse has failed three times to buy the LSE -- in 1998, then in 2000 and in 2005 -- as it sought to keep ahead of Euronext, which operates the Paris, Amsterdam, Brussels and Lisbon exchanges.