A Chinese official in charge of a massive water transfer scheme to supply the arid north urged faster work while another official confirmed on Tuesday that the project would be delayed four years until 2014.

The South-North Water Diversion Project to ease chronic water shortages in Beijing and other parts of northern China through two long canals has been troubled by pollution, difficulties relocating displaced residents and engineering hitches.

But Zhang Jiyao, head of the project, told his subordinates that there must be a "comprehensive acceleration of project construction", the project's website (www.nsbd.gov.cn) reported on Tuesday.

Zhang said the speed-up was needed to meet the needs of the country's north, contain costs and "protect social harmony and stability in the dammed area".

But Zhang did not repeat the previously set 2010 deadline for finishing the central route to carry water from tributaries of the Yangtze River in central Hubei province to Beijing.

An eastern route will draw directly from the Yangtze itself to the port city Tianjin and other parts of the north.

An official in the project's central office in Beijing later confirmed to Reuters that the scheduled time for finishing the 1,267 km (787 miles) central route had been pushed back four years.

"According to the latest plan, the central route will be finished in 2014," said the official, who refused to give his name. But he denied an earlier report that pollution worries were behind the delay.

Wang Fangyu, vice director of the Hubei section of the project, had said earlier this month that the delay was caused by pollution and ecological strains.

The Beijing-based official said that report was wrong, but also refused to explain the reason for the delay.

"What Hubei said is completely wrong," he said. "They are the local office, and they see things from a local perspective."