India said on Tuesday that 39 Indians, who were believed to have been kidnapped by Islamic State militants in Iraq in 2014, had been confirmed dead after their bodies were found.

The bodies were recovered from a mass grave and DNA tests had confirmed them to be those of the construction workers who went missing from the Iraqi city of Mosul, Foreign Minister Sushma Swaraj told parliament.

"With full proof I can say these 39 are dead," the minister said. The government had for years said it would only declare the men dead once it had full evidence.

Swaraj said the authorities in Baghdad helped identify a mass grave and with the help of deep penetration radar, the buried bodies were discovered and exhumed.

DNA testing provided matches for 38 of the missing men while one was a 70 percent match, Swaraj said.

"We recovered ID cards, long hair, kada and some non-Iraqi footwear," Swaraj said. A kada is a bracelet worn by Sikh men, who do not cut their hair.

Most of the workers were from the northern state of Punjab.

"Shattered at the heart-wrenching news ... that the 39 Indians missing in Iraq, most of whom were Punjabis, are dead," Punjab Chief Minister Amarinder Singh said on Twitter.

"My heart goes out to the families who had been living in hope since their reported abduction by ISIS in 2014."

The government had maintained for years that it believed the men were alive and it was trying to secure their release.

Opposition leaders and families of the men said the government had kept them in the dark.

"Why did the govt give false hope to the nation for three and a half years that the people were still alive? That was disappointing behaviour," Shashi Tharoor, a leader of the opposition Congress party, said in a tweet.