The board said it had accepted Finlayson's resignation for personal reasons.

The oil and gas major also warned that production would be at the lower end of its target range this year due to problems in Egypt and said it would hold off on 2015 guidance until it announces full-year results next February.

The company said 2014 production was expected at the lower end of its guidance of 590-630,000 barrels of oil equivalent per day.

Egyptian volumes in the first quarter were down 35 percent year on year.

BG, whose production troubles in Egypt have prompted it to cut its output outlook several times in the last two years, said it was committed to its strategy but would review its operational, investment and portfolio plans.

"The Board of Directors is fully committed to the group's strategy, which is built upon a portfolio of high-quality assets," said Chairman Andrew Gould, who will run the FTSE 100 company with immediate effect until a new chief executive is appointed.

"The company must accelerate the creation and delivery of longer-term value for our shareholders, while delivering the Group's business plans," Gould said.

"The Board felt that it was in the best interests of the group to accept Chris' resignation and seek fresh leadership to deliver both of these priorities."

Analysts at RBC Capital Markets said the review of assets would raise questions about the structure of BG.

"It may imply that previous statements from Chris Finlayson about not wishing to sell some of its stake in Brazil, for example, may be revisited," RBC said.

Other analysts welcomed the fact that the group said its major assets were performing in line.

BG shares fell 5.4 percent in early trade and were off 2.36 percent at 1,118 pence at 1015 GMT.

(Writing by Kate Holton and Karolin Schaps; editing by John Stonestreet and Jason Neely)

By Karolin Schaps