Gunmen shot dead a member of Mr Rao's Congress Party outside a voting centre in Patiali, near Agra, where rival party activists in state assembly elections fought pitched street battles. Armed thugs stormed scores of polling stations and tried forcibly to stamp ballot papers in favour of their candidates. The police opened fire to beat back the mobs.
Yesterday's was the 11th death in election-related violence in Uttar Pradesh during the past week. Officials say the others included two policemen and six candidates.
Voting in the state, which stretches from the Himalayan foothills across the Ganges plain, has been split over two days to aid security arrangements. Roughly half the region went to the polls last Thursday. The rest, including many known trouble spots, voted yesterday.
Trying to maintain calm on Thursday, state officials made over 47,000 'preventative arrests', seized large quantities of guns and explosives, and deployed over 60,000 security forces and another 325,000 police. The authorities also sealed off the border with neighbouring Bihar state to keep 'tough elements' from crossing over and rigging the ballots.
However, many of the 'tough elements' were already safely inside Uttar Pradesh and running for the state's 425 assembly seats. Along the Ganges river, in Varanasi, over 23 politicians charged with criminal activities, ranging from kidnapping, attempted murder and selling guns and pornography, are campaigning. They are backed by all the main Indian parties.
These by-elections in Uttar Pradesh, along with Rajasthan, Madhya Pradesh and Himachal Pradesh, were forced on the Indian voters when Mr Rao dissolved the four state assemblies in the wake of religious riots which followed the destruction last December of Ayodhya mosque by Hindu extremists. All these states were ruled by the main opposition party, the right-wing Hindu Bharatiya Janata Party (BJP).
Communal strife erupted with even greater ferocity in some states such as Maharashtra, which were governed by Mr Rao's Congress party, but no punishment fell on them.
The election result will not be released for another three weeks. If the ruling Congress party fares poorly, as some opinion polls suggest, Mr Rao's many enemies within the party will demand his resignation. Mr Rao, a prim and elderly politician, drew only meagre crowds while campaigning in Uttar Pradesh and other states. In rural areas many onlookers were more enthralled by the Prime Minister's shiny white helicopter than his election pledges.
The risks are equally high for the right-wing Hindu party. Its strategy has been to discard one of India's democratic cornerstones - that of secularism - and recapture the lost states as well as Delhi, which also faces local elections, by riding on a nationalistic Hindu wave. But Uttar Pradesh and the other states have large Muslim populations, and latest trends show that some voters are now wary of the widescale religious strife that might follow a BJP victory.
If the BJP does sweep back into the four states, the party's leaders, Lal Krishna Advani and Atal Behari Vajpayee, will undoubtedly raise a no-confidence motion before parliament, raising the possibility of early general elections.