The decision by Maldives is seen as an apparent snub to New Delhi which was critical of the Abdulla Yameen government for imposing emergency in the island nation earlier this year.
Sources told PTI that Maldives has conveyed to New Delhi that its defence minister would be travelling abroad and it would not be possible for him to lead a delegation to attend the expo, which will be held from April 11-14 in Thiruvidandai, south Chennai.
In February, Maldives had declined India's invitation to participate in the eight-day mega naval exercise -- Milan -- from March 6-13.
Ties between India and Maldives nosedived after Maldivian President Abdulla Yameen declared emergency on February 5 following an order by the country's Supreme Court to release a group of Opposition leaders, who had been convicted in widely criticised trials.
On February 21, India had reacted strongly over the extension of emergency by a month. The emergency was lifted 45 days later.
Interestingly, Pakistan Army Chief Qamar Javed Bajwa paid a rare visit to Maldives this week. Bajwa met Maldivian defence minister Adam Shareef Umar and called on Maldives President Yameen.
Sources said India has also invited China for the Defence Expo but there has not been any response from Beijing.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)