Oil thefts and gas supply disruptions in Nigeria contributed to a large fall in profits at Royal Dutch Shell in the second quarter.

Europe's biggest oil company was also hit by the tax impact of a weaker Australian dollar, with profits falling to $4.6bn (£3bn) from $6bn in the same period last year.

The results were worse than analysts expected, and were described by Shell's outgoing chief executive, Peter Voser, as "disappointing". Shell was among the biggest fallers in the FTSE 100 in early trading, down around 4%.

The company took a one-off hit of $2.2bn in the period, mainly related to the exploration and drilling of liquids-rich shale sites in North America. Profits were down 60% when the charge was included. "Higher costs, exploration charges, adverse currency exchange rate effects and challenges in Nigeria have hit our bottom line. These results were undermined by a number of factors – but they were clearly disappointing for Shell," said Voser.

He said Shell would "play our part" in Nigeria but added the company could not solve the problems alone.

Shell said it would accelerate the rate of disposals from the $21bn of assets it has sold over the past three years. It has launched a strategic review in North America and Nigeria, which will lead to further disposals.

The company said dividends paid out in the quarter totalled $2.8bn.