A section of the Great Wall was repaired in Suizhong county, Liaoning province, with what officials said was sand. But critics of the work said it was cement. zhang Shiyao / For China Daily

Repair work has severely damaged the natural image of the Great Wall in Suizhong county, Liaoning province, despite the work's strengthening effect, officials said.

"The restoration did follow the plan that we approved, and it also achieved its initial purpose to strengthen the wall. However, we can't avoid the severe problem it has brought to the image of the historic structure," Song Xinchao, deputy director of the State Administration of Cultural Heritage, said on Tuesday in Beijing.

Earlier this month, people posted pictures on social media and said the top of what they described as the "most beautiful" section of the Great Wall had been flattened so that it now looks like pavement and has lost its original character. The repair work to the section of the wall, built more than 600 years ago, was completed two years ago. It has irritated many netizens who question the project's legitimacy.

The administration sent a six-person team to Suizhong to investigate the project.

In announcing the results of the two-day investigation on Thursday, Lu Qiong, head of the team, said 780 meters of the Great Wall had been flattened with a mixture of lime, clay and fine sand.

On the surface of some steep parts, a small quantity of concrete was added to the traditional material, which was not clarified in the project plan, she said.

Fu Qingyuan, senior engineer with the State Research Institute of Cultural Heritage who was on the investigation team, said, "Concrete is internationally considered a new material that can be added to traditional material to improve the effect in restoring cultural relics."

Song said the administration should have supervised the concrete restoration of the Damaoshan section of the Great Wall after examining and approving the project's plan, which did not detail materials or methods.

Lu, the head of the investigation team, said in the report that the Cultural Relics Bureau in Liaoning needs to organize experts to fully examine the repair work to see whether there are more problems. Those responsible will be punished for the damage to the Great Wall's image, she added.