Sonia Gandhi, heir to India's Nehru-Gandhi dynasty, tearfully gave up her chance to become prime minister yesterday to protect her new Congress government from damaging attacks over her Italian birth.

Angry and upset, Congress lawmakers mobbed Ms Gandhi and begged her to change her decision, which paves the way for the architect of India's modern economic reforms, Manmohan Singh, to possibly take over the world's largest democracy.

But her shock move and the party's refusal to accept it has also left Congress without a leader to stake a claim to power.

"I must humbly decline this post," she told a chaotic party meeting in parliament's timber-panelled central hall, lined with life-sized portraits of former prime ministers, including her husband, Rajiv, and mother-in-law Indira Gandhi, who were both assassinated.

Some media said Ms Gandhi's politician children, son Rahul and daughter Priyanka, encouraged her to drop out, fearing she would become a target for Hindu extremists.

Fighting to make herself heard above indignant shouts from MPs, Ms Gandhi pleaded: "I request you to accept my decision and to recognise that I will not reverse it.

"It is my inner voice, my conscience," said the 57-year-old, who is an Indian citizen, adding she had never sought the top job and did not want her presence to weaken the government.

In a string of speeches marked by impassioned pleas, tears and breaking voices, Congress MPs said millions of ordinary Indians had chosen her to lead them and begged her to ignore attacks by Hindu nationalists over her foreign birth.

"Please remain with us, you cannot betray the people of India," said one emotional MP, Mani Shankar Aiyer, in the same hall where Ms Gandhi was anointed prime minister-elect three days ago. "The inner voice of the people of India is that you should be the prime minister."

Ms Gandhi, in a blue-lined cream sari, sat silently throughout, tears welling in her eyes. She rejected a unanimous party room motion to reconsider.

And the meeting broke up without choosing a replacement, leaving unanswered the question of who will ask President Abdul Kalam to let Congress and its allies take office, and when.

The decision by the head of the Nehru-Gandhi dynasty, India's equivalent of America's Kennedys, triggered anguished scenes at the red sandstone parliament complex and outside her home.

One man stood on the roof of a car, held a home-made gun to his head and waved a stick to deter people trying to calm him.

"Call Sonia Gandhi! Tell her I will kill myself if she doesn't become prime minister!" he said before being disarmed.

Others lay down in the street or torched effigies of Ms Gandhi's opponents, who have run a bitter campaign targeting her Italian background since their humiliating defeat in last week's poll.

Scattered protests were reported across the country. One Congress worker in the northern city of Kanpur doused himself with kerosene and tried to burn himself alive, but was stopped.

Another tried to jump from a building. Ms Gandhi would have been India's first foreign-born prime minister and the fourth from the Nehru-Gandhi clan after Rajiv, Indira and Indira's father, founding PM Jawaharlal Nehru.

Her withdrawal, and the prospect of Dr Singh leading Asia's third-largest economy, spurred markets, helping stocks on the Bombay exchange post their second-biggest daily rally just a day after the worst plunge in the exchange's 129-year history.

India's markets have been spooked by anti-reform comments by left-wing parties, which have more than 60 seats and are supporting Ms Gandhi without formally joining her coalition.

Markets welcomed Dr Singh's expected rise to power. "The father of India's reform programme rising to the prime ministership would be very positive from the standpoint of the market," said P.K. Basu, head of Robust Economic Analysis.

"But I would caution against excessive euphoria, since Dr Singh as an economic reformer is well regarded but his abilities as a political manager are untested.

"Sonia Gandhi has risen to the occasion and earned the gratitude and respect of most Indians with her magnanimous act," he said, adding her departure would remove a potential source of instability.