China has demanded that India immediately withdraw border troops that have crossed into Chinese territory, and cautioned India to avoid a "more serious situation and consequences".

Foreign Ministry spokesman Geng Shuang made the remark on Wednesday as Indian troops remained on Chinese soil after crossing the Sikkim section of the China-India border last month.

"China once again urges India to adhere to the boundary convention, respect China's territorial sovereignty and immediately pull back its troops to the Indian side to help solve the issue as soon as possible," Geng told a daily news conference in Beijing.

The Sikkim section of the China-India border was defined by the Convention Between Great Britain and China Relating to Sikkim and Tibet in 1890 and acknowledged by successive Indian governments.

China and India have been exploring solutions to their border disputes through meetings of special representatives and have jointly worked to maintain peace and stability in the border area.

However, Geng said, Indian troops illegally trespassing onto the Chinese side of the Sikkim section of the China-India border, which has long been demarcated, is a serious issue. China has strongly protested the incursion to India.

"We demand that India ... correct its mistake with practical action, in a show of its sincerity to solve border issues and develop the China-India relationship, in order to create the necessary atmosphere and conditions for the normal development of bilateral ties," he added.

On Tuesday, Chinese Ambassador to India Luo Zhaohui urged India to unconditionally withdraw its border troops to the Indian side of the border with China.

In an interview with the Press Trust of India news agency, Luo said he was deeply worried by the "grave" situation.

"It is the first time that Indian troops have crossed the mutually recognized boundary and trespassed into China's territory, triggering a close-range face off between Chinese and Indian border troops," he said.

"The first step is for Indian troops to unconditionally pull back onto the Indian side of the boundary. That is the precondition for any meaningful dialogue between China and India," he added.

Xinhua contributed to this story.

mojingxi@chinadaily.com.cn