Narendra Modi, widely tipped to become India's next prime minister, suffered a setback when his closest aide was banned from election rallies and meetings after a series of speeches deemed to have stoked tensions with Muslims.
Modi, 63, a pro-business Hindu nationalist, is the prime-ministerial candidate of the opposition Bharatiya Janata Party (BJP), which hopes to oust Rahul Gandhi's ruling Congress party with its promises of jobs and new infrastructure.
The aide, Amit Shah, who faces murder charges dating to his time serving under Modi in the state government of Gujarat, runs Modi's campaign in the state of Uttar Pradesh, which has a population larger than Brazil's and holds the keys to national power. Shah says the charges are a political conspiracy.
It was not immediately clear what impact a possibly disruptive ban on meetings in Uttar Pradesh by such a high-profile figure would have on Modi's campaign in the state. Shah is tipped to take up a senior role in any Modi government.
Uttar Pradesh, a northern state that is home to 200 million people, sends 80 lawmakers to Parliament - more than any other area. The BJP has never formed a national government without winning the most seats there.
The election commission ruled that both Shah and a minister in the Uttar Pradesh government had made statements that promoted "hatred and ill will" between religions and urged police to press criminal charges.
Speaking this month in an area of western Uttar Pradesh hit last year by deadly Hindu-Muslim riots, Shah was recorded telling voters to reject parties with Muslim candidates. He said Muslims in the area had raped, killed and humiliated Hindus.
Hindu-Muslim relations have been a key campaign issue, with critics accusing Modi of not doing enough to protect Muslims in unrest in Gujarat in 2002 that left at least 1,000 dead in revenge attacks. About 13 per cent of Indians are Muslim.
Modi denies that accusation or having any religious bias.
However, some of his supporters are openly anti-Muslim and Shah's canvassing has included accusing the state government of pandering to the Muslim vote at the cost of Hindu safety.
Shah has spent time in jail fighting charges that he ordered the extrajudicial killing of a man, the man's wife and a witness who were allegedly involved in organised crime but were accused of plotting to kill Modi. Shah is out on bail awaiting trial. He denies the charges against him.
The election commission applied the same restrictions on public meetings or road shows to another controversial politician, Azam Khan, who represents the Uttar Pradesh government and has verbally sparred with Shah.
"No permission should be granted for holding any public meetings, public processions, public rallies, road shows etc, by the district administration authorities, where the above two leaders are expected or likely to participate," the commission said in the statement, while asking the state administration to file a report and start criminal proceedings against Khan and Shah.
Khan has made a number of provocative statements in recent days to court the votes of Muslims - a significant vote bank in Uttar Pradesh.
Maoist rebels killed 14 people in two poll-related blasts in the insurgency-hit state of Chhattisgarh in central India. Five election officials and two bus drivers were killed when a landmine exploded under their vehicle in Bijapur district, where voting is to take place this week.
In another attack in the remote Darbha Forest in the south of the state, rebels killed five paramilitary soldiers and two civilians in an ambush on the soldiers' vehicle.