The gunbattle took place in a forest near Gudari village, close to the border with Chhattisgarh.
A police team led by District Superintendent of Police Akhileswar Singh, which included personnel from the district voluntary force, raided the site and retaliated when first fired upon by the extremists.
"We had information about the movement of Maoists in the area. Based on those inputs, we had launched the operation," Singh said.
"Thirteen bodies were recovered from the site," he said.
Police had earlier put the number of Maoists killed at 14.
This gunbattle is said to have caused the highest casualty among Maoist ranks in the state in recent years.
Police also recovered a huge cache of explosives, arms and ammunition from the site during a search after the gun battle. The seized items include one AK 47 and over a dozen locally made guns, besides two land mines, the officer said.
"It was a major success for the state police," state Director General of Police Prakash Mishra told reporters.
Among those killed were men suspected of involvement in the May 25 attack on a convoy of Congress leaders in neighbouring Chhattisgarh state, in which several Congress leaders of that state were killed.
A police team of Chhattisgarh is expected to reach the district headquarters town of Malkangiri late Saturday for further investigation.
Maoists are active in more than half of Odisha and the district of Malkangiri, over 600 km from state capital Bhubaneswar, is considered their stronghold.
--IANS (Posted on 14-09-2013)