Maharashtra Deputy Chief Minister Ajit Pawar resigned today bringing to fore strains in the coalition with Congress as 20 more NCP ministers offered to quit in a bid to put pressure on Chief Minister Prithviraj Chavan.

The 13-year-old coalition appeared to have hit a crisis with the resignation of Ajit, 53-year-old nephew of NCP chief Sharad Pawar, in the wake of media reports of scam in irrigation projects during his tenure as Water Resources minister between 1999 and 2009.

NCP suspects the hand of Congress behind these reports targeting Ajit and other NCP leaders.

However, Sharad Pawar dismissed reports of crisis or pressure building on him to get the party out of the coalition, saying there is no question of "destabilising" the government or any more resignations.

Ajit put in his papers today after discussions with his uncle in the wake of allegations of irregularities in clearing irrigation projects worth thousands of crores of rupees.

"I have sent my resignation to the Chief Minister's office....I am ready to face a CBI probe," Ajit told a hurriedly called press conference, adding he will stand vindicated.

His resignation comes on top of strains in the coalition. On a day of hectic developments, 20 other NCP ministers have sent their resignations to state party chief Madhukar Pichad with a demand that the party should quit the coalition.

The NCP legislature party will meet tomorrow to chalk out their future strategy.

Union Minister and NCP Vice President Praful Patel spoke of a "big conspiracy" to defame the NCP not only by opposition parties but also by "our friends".

He dismissed as baseless reports that the resignation would pave the way Sharad Pawar's daughter Supriya Sule replacing Ajit as Deputy Chief Minister.

Ajit, who held Finance and Energy portfolios, said he will continue to be the leader of NCP legislature party as long as he enjoyed the support of the legislators. He would not accept any post till his name is "cleared", he said.

There have been reports in the media that Ajit had cleared 38 projects worth Rs 20,000 crore in 2009 without clearance of Governing Council of Vidarbha Irrigation Development Corporation (VIDC).

"People are jealous of the rise of NCP," Ajit said, in an apparent reference to ally Congress with which his party has had an uneasy relation for the last several years.

Sharad Pawar said he had given "permission" to Ajit to resign after he had called him yesterday and sought clearance. "There is no question of supporting the government from outside. We will be part of the government," he said.

The Union Minister said Ajit told him that he was ready for a probe and confident of coming out clean in the alleged "irrigation scam" during his tenure as the state's Water Resources Minister.

The NCP supremo said Ajit felt it was improper for him to continue in office while allegations against him were being probed.

Sharad Pawar, who is in Kolkata to attend a conference, said he would go to Mumbai and discuss the issue with colleagues and sort it out.

In Delhi, Patel dismissed speculation about today's development as an uncle versus nephew affair. He said the party backed Ajit's decision and there is no going back on it.

He talked to Chief Minister Chavan and pressed for an early publication of the 'White Paper' on the alleged irrigation scam so that truth will come out.

Sharad Pawar said it is a "conscious decision" of the party to continue in the coalition.

This is the first major trouble between the Congress and the NCP after Chavan took over as Chief Minister in November, 2010 replacing Ashok Chavan who quit in the wake of the Adarsh housing scam.

The last few months had witnessed several NGOs in Maharashtra as also Kirit Somaiya of BJP attacking a number of NCP ministers including Ajit, Chagan Bhujbal and Sunil Tatkare amidst suspicion in NCP that Congress was conspiring to defame it.

When contacted by PTI, Chavan said, "I am not in a position to comment on this development right now. I will speak to all concerned and then respond."

Chavan's announcement to bring a white paper on the status of irrigation projects after state's economic survey said only 0.1 per cent additional area was brought under irrigation in a decade despite a whopping Rs 72,000 crore being spent during the period, had also reportedly riled the NCP.