Iran's main economic partner China has invested more than $40 billion in the Islamic republic's oil and gas sector, according to a senior Iranian official.

China has also put forward proposals to participate in building seven new refineries in Iran, the country's Deputy Oil Minister Hossein Noqrehkar Shirazi was quoted as saying in the Gulf Daily News, our sister publication.

On the import volume, the minister said Tehran's oil exports to China fell by 30 per cent in the first six months of the year compared with the corresponding period last year.

'The volume of oil exports to China in the first six months of this year decreased to less than 9.02 million tonnes or 66.12 million barrels. This shows a 30 per cent decrease' over the first half of 2009,' he added.

Iran, Opec's second largest oil exporter, has a dilapidated refining sector, forcing it to import petroleum products such as gasoline to meet domestic needs.

'The volume of Chinese investment in upstream projects is more than $29 billion,' Noqrehkar Shirazi told Mehr news agency, adding that Beijing had signed contracts worth another more than $10 billion in petrochemicals, refineries and oil and gas pipeline projects.

Noqrehkar Shirazi said that Chinese imports of Iranian oil fell in the first half of the year.

'Although Iran is still among top 10 oil exporters to China, it is the only country which in the first six months of 2010 has seen its exports to China falling,' he said.

In recent years, China has filled the gaps in Iran's energy sector left by Western firms forced out by international sanctions.

In 2009, China became Iran's premier trading partner, with bilateral trade worth $21.2 billion against $14.4 billion three years earlier.

Commercial ties between the two countries were almost non-existent 15 years ago, amounting to just $400 million.

According to official data, Western sanctions opened the way for Chinese companies, which last year directly supplied Iran with 13 per cent ($7.9 billion) of its imports.

Iranian estimates also suggest that an equivalent amount was imported indirectly through the UAE in 2009.

China backed the fourth set of UN sanctions against Iran over its contested nuclear programme, but Beijing has consistently urged the world powers to resolve the crisis diplomatically.

On Friday, it also opposed the latest unilateral sanctions on Iran imposed by the European Union.