In a major blow to the Aam Aadmi Party (AAP), senior minister and long-term party leader Kailash Gahlot has resigned.

According to reports, he is likely to join the Bharatiya Janata Party (BJP).

The setback for AAP comes just months ahead of the Delhi Assembly polls.

Gahlot was heading key portfolios in the Delhi government, including Home, transport, IT and Women and Child Development.

In his resignation letter addressed to AAP convener Arvind Kejriwal, Gahlot said he was facing "grave challenges" within the party.

"Political ambitions have overtaken our commitment towards people, leaving many promises unfulfilled. Take for example the Yamuna, which we had promised to transform into a clean river, but never got around to doing it. Now the Yamuna River is perhaps even more polluted than ever before," he has said.

Taking an indirect dig at Kejriwal, he has referred to "many embarrassing and awkward controversies like the Sheeshmahal"- a term used by the BJP to refer to the Chief Minister's residence renovation during the AAP's supremo's term.

He has said such controversies "are now making everyone doubt whether we still believe in being the Aam Aadmi".

Gahlot alleged that AAP has been "fighting for its own political agenda" and this has "severely crippled our ability to even deliver basic services to the people of Delhi".

"It is now obvious that real progress for Delhi cannot happen if the Delhi Government spends majority of its time fighting with the Centre," he has said.