Mumbai, June 19 - Giving a major boost to UPA Presidential candidate Pranab Mukherjee, key NDA constituent Shiv Sena has assured him of its support in his bid for the top constitutional post.

"The Sena will support Pranab Mukherjee (in the Presidential polls)," Sena spokesperson Sanjay Raut told PTI.

The assurance was given to Mukherjee, who called up Sena chief Bal Thackeray and his son Uddhav Thackeray, the party Executive President, yesterday, Sena sources said.

Sena, the oldest ideological ally of BJP, was understood to be concerned over the approach of NDA to the Presidential polls and disappointed about the fact that the alliance has not been able finalise its candidate.

Shiv Sena had supported Pratibha Patil in 2007, breaking ranks with BJP as Patil hailed from Maharashtra.

BJP and other NDA constituents had at that time backed late Bhairon Singh Shekhawat for the post of President. PTI