Chinese officials also said the "atmosphere is not right" for a meeting between Modi and Xi on the margins of the G20 Summit beginning on Friday.
"The 1890 convention said that the Sikkim section of the boundary commences from East mountain and the incident (of road building) took place about 2,000 meters away from Mount Gipmochi", Geng had asserted.
"In addition, he will also participate in the BRICS Leaders' meeting".
Around 3,000 troops from both countries are reportedly stationed near Doklam, an area said to be around 15km north of Gamochen.
Beijing, in turn, has accused India of violating an 1890 border agreement between the United Kingdom and China that previous Indian governments have pledged to uphold, and it should be respected to end a "very serious" incursion by India.
The month-long standoff - and unconfirmed reports of troop buildups on both sides of the border - has also underscored the swiftly deteriorating relations between the two Asian rivals.
India's Ministry of External Affairs referred to a statement it made last week, when it warned China that construction of the road near their common border would have serious security implications.
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If the tensions escalate and trade channels are disrupted, then both nations are likely to suffer significant monetary losses. The military build-up in the South China Sea has made the Indians even more suspicious of all Chinese military manoeuvres.
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Duterte also said he is not happy with the way the government has suffered casualties during the conflict. He said he felt "more in shame" for sending soldiers to the war that caused the loss of precious lives.
The state-run Global Times went a step further on Thursday, calling of Sikkim's "independence" and separation from India. "Nowadays, the situation is entirely different from 1962, so we hope India will not do anything irrational for its own good, otherwise it will pay more than in the past", Hu Zhiyong, a research fellow at the state funded Shanghai Academy of Social Sciences, said.
"The papers that served up new rhetoric about the 20-day-old dispute include the state-run Global Times which said in an editorial that India will confront "greater losses" than in the 1962 war if it "incites" border clashes with China".
The Chinese political counsellor said that following the face-off the Indian side has claimed that Doklam belongs to Bhutan and that China "changed the status quo" of the area and New Delhi cited its security concern.
China and India have been engaged in a standoff in Dokalam near the Bhutan tri-junction for the past three weeks after a Chinese Army's construction party attempted to build a road.
"Perhaps its defeat in that war was too humiliating for some in the Indian military and that is why they are talking belligerently this time", it said. China used its government-controlled media to bully India with a threat of a war. If India loses in the Doklam confrontation, two things will happen: since the territory is disputed by Bhutan and Bhutan relies on India for protecting its territorial integrity and sovereignty, Thimpu will feel let down by India.
"India has startling control and oppression over Bhutan, and as a result, Bhutan has not established diplomatic ties with its neighbor China or any other permanent member of the UN Security Council".