Amid buzz that he may be made a minister in the union cabinet, Rashtriya Lok Dal (RLD) leader Ajit Singh on Saturday met Congress president Sonia Gandhi in New Delhi and sealed his party's tie-up with the Congress for the coming Uttar Pradesh Assembly polls.

"Sonia Gandhi has accepted in principle to make RLD a constituent of the United Progressive Alliance (UPA)," Congress general secretary Janardhan Dwivedi told reporters after the meeting.

Ajit Singh will write a letter to Gandhi, who is also the UPA chairperson, and the formalities of his party's entry into the UPA will be undertaken, Dwivedi added.

After the UPA admits the RLD into its fold, Ajit Singh will be offered a cabinet post, sources said.

The RLD, which had an electoral understanding with the BJP in the 2009 Lok Sabha polls, had won five seats. Both Ajit Singh and his son, Jayant Chaudhary, are Lok Sabha members.

Congress general secretary Digvijay Singh also said that the electoral deal with the RLD has been approved.

The deal was reached at a meeting between Ajit Singh and Congress general secretary Rahul Gandhi on Friday, according to the sources.

The RLD will be allotted 40-50 seats for the coming Uttar Pradesh assembly polls, it is learnt. The state has 403 assembly constituencies.

RLD sources said Ajit Singh was expecting a ministry which suits his "seniority and experience". He will be sworn in as a minister this month, they added.