After throwing enough hints that she was ready to do business with the ruling alliance, Uttar Pradesh Chief Minister Mayawati on Friday met Congress president Sonia Gandhi, marking the first moves that could throw up a combined candidate of the UPA-Left-BSP for the presidential poll.

Both Mayawati, on her first visit to New Delhi after assuming power in UP, and Congress were silent on what transpired at the nearly 100-minute meeting held in the backdrop of hectic efforts by UPA leadership to bring BSP on board on the issue of a successor to A P J Abdul Kalam.

Mayawati's party holds the key in the presidential poll given the fact that the candidate of the ruling alliance can succeed only with the full backing of the Left and the BSP.

Sonia took the opportunity of inviting Mayawati for tea at 10 Janpath, and there could have been substantive talks given the BSP supremo's earlier indications that she would only engage with the UPA in the matter and has nothing to do with the opposition NDA.

During her two-day stay, Mayawati said she would interact only with two leaders -- having tea with Sonia and a meeting with Prime Minister Manmohan Singh on Saturday.

Maintaining that she was supporting the Congress-led coalition at the Centre to keep 'communal forces' at bay, Mayawati said her party was an outside supporter of the Congress-led coalition at the Centre and this would continue.

She rejected suggestions of her party joining the Centre.

"I will be able to open my cards (on the presidential polls) only after consultations with party parliamentarians, legislators and other leaders. I know this is a very important issue and a decision needs to be taken carefully," she said.

Sonia and Dr Singh have been holding consultations with various parties on the presidential poll issue and the names of senior Ministers Pranab Mukherjee and Sushil Kumar Shinde as also Congress leader Karan Singh are doing the rounds.

Mayawati, whose party's spectacular victory in the assembly polls made her a key player in the race for the presidency, had so far not revealed her cards.

Meanwhile, the CPI-M, which threw the ball in the Congress court on the presidential candidate, on Friday stepped up pressure on it saying there will be 'no compromise' on the criteria laid out by Left parties for their support.

The issue of presidential election came up for discussion at the CPI-M's two-day Polit Bureau meeting which began in New Delhi and the unanimous view was that the candidate should be secular and have the widest possible acceptance.

The CPI-M had publicly favoured External Affairs Minister Pranab Mukherjee for the top job but the Congress has itself clarified that there was no decision by it on any particular candidate.

Senior party leader Sitaram Yechury said discussions are on with all 'friendly parties' and the idea is to have a candidate with impeccable secular credentials, understanding of political complexities and who could ensure balance between the Judiciary, Parliament and the Executive.

It is unclear whether the call for a consensus by former Prime Minister Atal Bihari Vajpayee, who has been authorised by the NDA to decide on the issue, evoked any response from the UPA.

The CPI-M sounded unenthusiastic about Vajpayee's suggestion.