India's nominee for the post of United Nations Secretary-General, Shashi Tharoor, and South Korean Foreign Minister Ban Ki Moon have emerged key contenders among the four declared candidates for the top post in the first informal poll held by the 15-member Security Council.

While Tharoor got second highest endorsements after Moon in the straw poll held on Monday night, Thai Deputy Prime Minister Surakiart Sathirathai and Sri Lankan Jayantha Dhanapala got third and fourth places in the poll, diplomats said.

The straw poll marked the beginning of the selection process, which could last till October. New candidates can be introduced at any stage till the final selection is made. The new Secretary-General is to take over on January 1 next year from incumbent Kofi Annan who retires after completing two terms on December 31 this year.

Under a new procedure adopted by the Council, the ballot of each candidate had three boxes 'encourage,' 'discourage' and 'no opinion.' The members were expected to check one box.

Tharoor received 10 'encouragements,' two 'discouragements' and three 'no opinions.' Moon got 12 'encouragements,' one 'discouragements' and three 'no opinions' to emerge the top contender.

Sathirathai, who has been endorsed by ASEAN, received seven 'encouragements,' three 'discouragements' and five 'no opinions.' Dhanapala, a former UN disarmament under secretary-general, could manage only five 'encouragements' but got six 'discouragements' and four 'no opinions' to finish at the bottom.

Each member of the Council votes separately for each candidate. Thus one member can vote 'encouragement' for more than one candidate. However, it was not clear how the five veto-wielding permanent members voted as all members were given similar ballots.

At a later stage, the permanent members would be given ballots of different colour or asked to mark the ballot in a different colour ink to establish if any candidate has attracted veto. That would be an important stage for candidates to determine their viability.

The voting was secret and the results were to be officially communicated only to the Ambassadors of the countries whose have fielded the candidate to enable them to decide whether or not they want their candidate to continue in the fray. The Council officially did not announce the results but diplomats coming out of the Council informally briefed reporters about how the candidates were placed.