However, their influence has somewhat diminished after they were returned in only 42 seats in these elections - down from 48 last time.

Made up of the Communist Party of India (Marxist), Communist Party of India, the All India Forward Bloc and the Revolutionary Socialist Party, the left's key strongholds are the southern state of Kerala and the eastern state of West Bengal.

They also have a presence in Andhra Pradesh, Bihar, Tamil Nadu and Tripura.

But the communists suffered a few setbacks in these elections especially in West Bengal, Bihar and Andhra Pradesh. Their power base in West Bengal eroded somewhat, following a successful challenge posed by the BJP and its regional ally, the Trinamool Congress.

They have also slipped in Bihar and Andhra Pradesh, where their constituent parties failed to win any seats. However, the communists are still strong in Kerala and Tripura.

The CPI was the first communist party to formally join an Indian federal government, when they were part of the government of prime minister Deve Gowda in 1996.

A move to make veteran communist leader, Jyoti Basu, prime minister at the time came unstuck when his party, the CPI(M), rejected the move.

Although the communist parties have traditionally been opponents of Congress, they have identified the Hindu nationalist BJP as their key political enemy.