The unprovoked assault on the labourers were carried out by heavily armed suspected NSCN (IM) militants numbering around 15, the officer said.
The assaulted labourers, hailing from Heirok village and belonging to one ethnic group, were engaged in repair work of a dam damaged during last year's massive flooding in Thoubal district, the sources said.
One of the assaulted labourers was rushed to Imphal for treatment as his condition had deteriorated, the officer said.
The place is the assembly constituency of Manipur's education minister Moirangthem Okendro.
In the second incident, some teachers of Heirok Higher Secondary School, who visited a tourist park for leisure, near the dam site, were robbed of Rs 2 lakh while six mobile phones were forcibly taken away by the same group of militants elsewhere in the district, another police officer said.
The militants also fired around six rounds at a motor boat kept at the park which is under construction.
On hearing about the incidents, large number of people from Heirok came and picked up around 20 persons returning to their homes towards the villages on the suspicion of they being involved with the NSCN (IM).
