The Dutch national airliner, KLM, has announced a global alliance with its Italian counterpart, Alitalia.

The deal, which includes both passenger and cargo activity, will come into effect next year, but is said to be conditional on substantial privatisation of Alitalia.

The companies' executives said cooperation would be on a scale and intensity that was unique in the aviation world.

Under the deal, Alitalia will also join KLM's partnership with the US airline Northwest, which is expected to open the North Atlantic market for the Italian carrier.The BBC business reporter says the agreement is part of a worldwide trend towards such alliances.

He says the trend has been criticised by some groups who fear it will undermine competition.