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Five policemen have died and more than 50 people have been injured, the Assam government said. The Superintendent of Police in Cachar district sustained bullet injuries.
Chief Minister Himanta Biswa Sarma, who will visit Silchar today, tweeted that "clear evidences are emerging" that the Mizoram Police used Light Machine Guns against the Assam Police personnel. "This is sad, unfortunate and speaks volumes about the intention and gravity of the situation," his tweet read.
In a statement, Assam accused Mizoram of building a road destroying a Reserve Forest area in Lailapur and setting up an armed camp. The state said their police forces were attacked by miscreants and later, the Mizoram police when they went to resolve the situation.
Mizoram said the violence started after the Assam Police crossed the border and "over-ran" a police post at Kolasib. Mizoram also said the Assam Police damaged vehicles on the national highway and opened fire on the state police.
The violence took place two days after Union Home Minister Amit Shah met all Chief Ministers of the northeast at Shillong. On Monday, Mr Shah dialled Chief Ministers of both states and asked them to resolve the border issue, reported news agency ANI.
Earlier, Mr Sarma and Mizoram Chief Minister Zoramthanga clashed on Twitter, posting videos of the violence and sought Mr Shah's intervention.
"Kolasib SP is asking us to withdraw from our post until then their civilians won't listen nor stop violence," Mr Sarma had tweeted. Mr Zoramthanga responded with some videos, one of which was of a car apparently targeted on the highway.
Three districts of Mizoram -- Aizawl, Kolasib and Mamit -- share a 164.6 km long inter-state border with Assam's Cachar, Hailakandi and Karimganj districts.
The area has seen clashes for decades, with the locals and security forces on each side accusing the other of intrusion. The last incident was reported in June.
The Mizoram government has constituted a boundary commission to deal with demarcation of the border. Assam has border disputes with Meghalaya and Arunachal Pradesh as well.