Opec delivered only a limited increase in oil production in September, a Reuters survey has found, as a cut in Iranian shipments due to US sanctions offset higher output in Libya, Saudi Arabia and Angola.

The 15-member Organization of the Petroleum Exporting Countries pumped 32.85 million barrels per day in September, the survey on Monday found, up 90,000 bpd from August's revised level and the highest this year.

But the 12 Opec members bound by a supply-limiting agreement actually cut output by 70,000 bpd because of declines in Iran and Venezuela, boosting compliance with supply targets to 128 percent from a revised 122 percent in August, the survey found.

Oil prices have extended a rally this year on expectations the sanctions on Iran will test Opec's ability to replace the shortfall, despite the group agreeing in June to pump more after pressure from US President Donald Trump. Oil LCOc1 on Monday reached $83.32 a barrel, the highest since 2014.