Oil giant Royal Dutch Shell has said it plans to cut 6,500 jobs this year.

The firm said it was taking action amid a slump in oil prices and that it was "planning for a prolonged downturn" as it slashed costs for 2015 by 10% or four billion US dollars (£2.6 billion).

Investment for the year is being pared by a fifth or seven billion US dollars (£4.5 billion). Further cost-cutting is expected in 2016.

Chief executive Ben van Beurden said: "We have to be resilient in a world where oil prices remain low for some time, whilst keeping an eye on recovery."

It is the first time that Shell has put a number on total job cuts for 2015, though it said that the majority of jobs within that had already been announced, including the loss of 500 in the UK plus others in Norway, the US and Nigeria.

The global workforce today stands at 94,000.

Mr van Beurden said Shell was making good progress on its planned £47 billion takeover of BG.

He said Shell was aiming to become a "simpler and more profitable company" - and after the transaction would cut spending on exploration while reviewing the way it invests capital in long-term projects and disposing of assets.

"These are challenging times for the industry, and we are responding with urgency and determination, but also with a great sense of excitement for the future."

Shell disclosed the figures as it published second quarter results showing a 35% fall in earnings to 3.36 billion US dollars (£2.16 billion).

It said profits in its "upstream" production and exploration division were weighed down by "the significant decline in oil and gas prices and decreased production volumes" partly offset by lower costs.

Earnings from the division fell by 80% to 774 million US dollars (£496 million).

The price of a barrel of Brent crude has slumped by more than half from nearly 116 US dollars in June last year.

It has recovered a little from a low of 45 US dollars in January but the continuing prospect of a glut of supply in world markets - especially after a thawing in relations between the US and sanctions-hit Iran - has kept this in check.

Brent crude reached nearly 70 US dollars in May but has since fallen again to around 53 US dollars.

But Shell said downstream results were strong as it took steps to improve financial performance and higher profit margins from its refining business.

The downstream business also includes the selling of fuels and other products for home, transport and industrial use.

Profits from this division were up 116% to 2.75 billion US dollars (£1.76 billion) in the quarter.

Shell's swoop for BG, announced earlier this year, is the biggest takeover in the sector since US firm Exxon's purchase of Mobil in 1998.

It said it remained on track to complete the deal in early 2016 and said it had received approvals from regulators in Brazil, South Korea and the US.

Shell said it expects to see 30 billion US dollars (£19 billion) of asset sales between 2016 and 2018 "as the combined portfolios are restructured".

The company said it had agreed to sell a 33% stake in Japan's Showa Shell Sekiyu for around 1.4 billion US dollars (£900 million).