Al Jazeera's Prerna Suri said the surrender had been confirmed by officials and would be a major blow to ULFA, which has seen several of its senior commanders arrested in the past year.
After Friday's surrender, the only senior ULFA leader at large is Paresh Baruah, a military commander. Officials believe that he too may soon surrender.
"We have information that Paresh Baruah is currently based on the China-Myanmar border and hope he will accept our standing offer of peace talks," Tarun Gogoi, Assam's chief minister, said.
ULFA has fought for the past two decades for an independent homeland for ethnic Assamese people living in India's northeast.
At least 10,000 people, most of them civilians, have died in Assam state because of violence between government forces and ULFA fighters, as well as with the National Democratic Front of Boroland, another separatist group.