Royal Dutch Shell plans to put three oil and gas assets in the North Sea up for sale, as it seeks to ramp up disposals and focus on improving shareholder returns after a shock profit warning.

Like its industry peers, Shell has been facing increasing investor pressure to rein in spending as costs rise and prospects for oil prices wane.

Glen Cayley, the Anglo-Dutch company's vice-president of its upstream business in Europe, has spoken to staff about the proposed sell-off of its Anasuria, Nelson and Sean platforms in the British part of the North Sea.

Together, the assets account for about two per cent of Britain's oil production.

Output from the North Sea basin has been in decline since 1999, raising concerns that the biggest oil companies could turn their backs on it, but Shell said it was committed to the area.

Shell, attempting to win round investors after a major profit warning early this year, said it was targeting $15 billion of disposals over the next two years as it tries to deliver more attractive returns to shareholders.

According to a report in Britain's Guardian newspaper, the North Sea disposals were not influenced by the upcoming September 18 referendum on Scottish independence, which other energy bosses have signalled is further undermining the North Sea investment climate.

The boss of BP, a big investor in Britain's North Sea waters and the country's second biggest oil company, warned last week that Scottish independence could cause his company "uncertainties".

Over the last four years, Shell's total average production from Britain's North Sea has been around 136,500 barrels of oil equivalent per day. Britain in total produced around 1.55 million barrels of oil equivalent per day in 2012.-Reuters