World shares and the dollar tumbled on Friday and oil and gold jumped after U.S. President Barack Obama authorized targeted air strikes in Iraq, raising worries of another drawn-out conflict in the region. It came as fighting also resumed in Gaza between Palestinian militants and Israel and with NATO’s calls for Russia to “step back from the brink” of war in Ukraine still ringing in ears of volatile markets. “Earlier this week, one Iraqi in the area cried to the world, ‘There is no one coming to help’,” said Obama, who has been reluctant to go back into Iraq having withdrawn in 2011.