China National Petroleum Corp will shut its regional representative offices and cut overseas branches as the nation's biggest explorer tightens internal regulations to fight corruption.

"Because of the large amount of hotels and representative offices we run, it's easy for irregularities to happen and cause problems," CNPC said in a statement on Monday.

The Beijing-based company will close offices in Shanghai, Guangzhou and Wuhan by year-end and sell most hotel assets by 2017, other than those in remote areas that serve its oil and gas fields. It will also reduce the number of overseas offices by 38 percent.