New Delhi, Mar 14 (IANS): The Congress party Thursday congratulated its chief Sonia Gandhi for having completed 15 years in office, making her the longest serving president of the 127-year-old party.

"We felicitate Sonia Gandhi's continued effort and support in leading the party," Congress spokesperson P.C. Chacko told reporters.

Several Congress leaders including Communications and IT Minister Kapil Sibal, Delhi Chief Minister Sheila Dikshit and Minister of State for Parliamentary Affairs Rajeev Shukla congratulated her at her official residence.

"We thanked her for leading the party and strengthening it. Her contribution for the party is worth praising. All the MPs (members of parliament), MLAs (members of legislative assemblies) and ministers have praised her efforts and for leading the party in tough times," Shukla told reporters.

Though some leaders planned to celebrate the occasion in a big way, Sonia Gandhi reportedly asked them to refrain keeping in mind the drought prevailing in some parts of the country.

Sonia Gandhi, who took office as Congress chief in 1998, led the party to victory in 2004 with the formation of the Congress-led United Progressive Alliance government, which continues in office under Prime Minister Manmohan Singh.

Setting an example in 2004, Gandhi decided not to become the prime minister and instead appointed her confidante Manmohan Singh as the head of the coalition government.

After the assassination of her husband and former prime minister Rajiv Gandhi in 1991, Sonia Gandhi withdrew from active politics for seven years but decided to take the plunge by campaigning for the party in the 1997 general elections.

The party, then headed by Sitaram Kesri, fared poorly at the hustings leading to his exit.

Sonia Gandhi's entry energised a demoralised Congress and the party was able to improve its presence in many states since then. Her current term expires in 2015.