Oil and gas firm Tullow Oil has seen its pre-tax loss fall to $908m in 2016, mainly as a result of a sharp drop in impairment charges.

The London-based firm had reported losses of $1.3bn in 2015.

Revenue fell 21% from a year earlier to $1.27bn, while impairment charges shrank by more than half to $168m.

Tullow's oil production in West Africa averaged 65,000 barrels per day in 2016 and this is expected to rise to an average of between 78,000 and 85,000 bopd in the current year.

The company's share price fell more than 5% in London following the release of the earnings results.

"The clear highlight of 2016 was delivering Ghana's second major oil and gas development, the TEN fields, on time and on budget," chief executive Aidan Heavey said.

"Production from TEN, alongside our other West African oil production, has provided Tullow with positive free cash flow and enabled us to begin the important process of deleveraging our balance sheet."

Tullow's gas production in Europe averaged 6,200 barrels of oil equivalent per day in 2016.

The firm announced that no annual dividend would be paid to shareholders.

"At a time when Tullow is focusing on capital allocation, financial flexibility and cost reductions, the board believes that Tullow and its shareholders are better served by retaining funds in the business," it said.