SHANGHAI (Reuters) - China’s environment ministry said it will send 5,600 inspectors on a year-long investigation into the sources of air pollution in major northern cities.

The Ministry of Environmental Protection (MEP) said in a notice posted late on Wednesday on its official website (www.mep.gov.cn) that inspections into 28 northern cities in and around the Beijing-Tianjin-Hebei region will focus on improving the way the country's standards and laws are enforced.

The 28 cities have already pledged to draw up detailed action plans to address smog, promising to shut small polluting enterprises and halve coal and steel production in the winter.

The region is a frontline in China’s “war on pollution”, but despite improvements last year it saw average concentrations of breathable particles known as PM2.5 rise 48 percent in the first two months of 2017.

The notice said the latest campaign, described as the largest ever undertaken, would seek to “normalize compliance” in a region frequently accused of turning a blind eye to polluters in order to protect jobs and revenues.

The ministry has routinely named and shamed local governments and enterprises in northern China for failing to comply with anti-smog regulations.

China is also launching a new round of inspections that will focus on overall environmental compliance in 15 provinces and regions, including the city of Shanghai, Liaoning in the northeast and the island of Hainan on the southeast coast.

The first round of inspections last year, which covered big coal-producing regions like Inner Mongolia, Ningxia and Shanxi, showed that progress had been made in the battle against air pollution, but water quality in some areas had deteriorated sharply.