US crude oil retreated below the $70-a-barrel mark on Tuesday following cautious comments from Opec, the oil producers’ group, which warned that sustaining prices at current levels would depend on “clearer signs of improvement in the global economy”.

Nymex September West Texas Intermediate fell $1.15 to $69.45 a barrel and ICE September Brent lost $1.04 to $72.46 a barrel.