Iran plans to invest $18 billion by 2015 to boost output the oil-rich south and expects its Yadavaran field to start production in a few months, the Iranian Oil Ministry's website Shana said on Sunday.

Opec's second largest producer, which again rejected calls for a coordinated production increase on Saturday, pumped a near-capacity 3.6 million barrels of crude a day (bpd) in June.

US sanctions over Tehran's disputed nuclear programme have prevented western firms from investing in the Islamic Republic and dampened Chinese enthusiasm for tapping some of the world's biggest oil and gas reserves.

Tehran warned China National Petroleum Corporation  in June it would cancel a deal to develop Iran's South Pars gas field if CNPC continued to delay the project.

The majority of the $18-billion spending plan to 2015 will now be met by Iran, the country's deputy oil minister said in a ministry news note published on Sunday, adding that about $3 billion would be spent on southern projects by next March.

"Many plans are being implemented to accelerate development of shared oil and gas fields while the ministry aims to increase oil production in the oil rich region of the south to three million barrels per day," deputy oil minister Mohsen Khojasteh Mehr told Shana.

The Yadavaran oil field being developed by Iran's National Oil Company (NIOC) and China's Sinopec will start production this autumn at around 20,000 bpd and climb to its expected ceiling of 85,000 bpd over the next two years, he said.

China is one of the biggest buyers of Iranian crude oil and its top energy company CNPC has deals to boost output at Iran's North Azadegan oil field and South Pars gas field.

But despite its still voracious appetite for energy, China's top energy firms are thought to be slowing projects in politically isolated Iran as their ties with US energy companies strengthen while booming North American gas output swells global supply.                      

Rejecting pressure from consuming countries for Opec producers to raise production targets at their next meeting scheduled for December 14, Iran's caretaker oil minister Mohammad Aliabadi said on Saturday the oil exporter's group Iran currently heads would oppose any increase.     

"Iran's policy as head of Opec is to maintain the production ceiling of this organisation," Aliabadi was quoted as saying by the semi-official Mehr news agency.

"It is an issue which a majority of Opec members agree with." - Reuters