China's crude oil imports from Iran fell around a quarter in September from a year earlier, data showed on Wednesday, as traders cited delivery delays by Iranian tankers because of Western sanctions and a cut in condensate imports.

China, Iran's top oil customer, bought 1.57 million tonnes of Iranian crude in September, equivalent to about 382,400 barrels per day (bpd), up 3 percent from 371,000 bpd in August, according to data from the General Administration of Customs.

China imported 504,000 bpd of Iranian crude in September 2011.

Imports for the first nine months totalled 420,800 bpd, 22 percent below year-earlier levels, largely because of steep cuts made in the first quarter as China and Iran wrangled over contract terms.

Sinopec , Asia's biggest refiner, halted purchases of condensate from Iran's South Pars field from July through September, partly because of a planned refinery overhaul, industry sources said.

Imports also declined because Iran's tanker fleet, the sole transporter of its crude to China since July, has been struggling to meet delivery schedules, trade sources said.

Iran, grappling with tough Western sanctions targeting its energy and petrochemical sectors, has delayed loading of some shipments for September, October and November to China, as a result of the inability of Iran's shipping fleet to cope with exports, trading sources have told Reuters.

The delays are further evidence the National Iranian Tanker Company (NITC) is struggling to meet delivery schedules after a European Union insurance ban caused buyers to cut back on orders, forcing the company to deploy more than half of its tanker fleet to store oil.

Exports from Iran, once the world's fourth-largest exporter, slumped to a new low of 860,000 barrels per day (bpd) in September, compared with 2.2 million bpd at the end of 2011, the International Energy Agency (IEA) said.