At least 31 have died, including an imam, in clashes between Muslims and Hindus in the city of Muzaffarnagar and other areas, Union Principal Secretary Home R. M. Srivastava said.
Among the dead is a television journalist covering the clashes that began Saturday in Muzaffarnagar city, about 80 miles northeast of New Delhi.
The unrest was sparked by the killing of three villagers who objected to the harassment of a young woman in northern India, the Times of India reported.
Violence spread to Muzaffarnagar's neighboring district of Shamli Monday where a 40-year-old imam of a mosque was shot dead, Shamli district magistrate P.K. Singh said.
A curfew remained in place and the army patrolled the streets of Muzaffarnagar for the second consecutive day.
Union Minister of State for Home R.P.N. Singh said 5,000 paramilitary force personnel had been sent to help military patrols in violence-hit areas outside the Muzaffarnagar district.
"If necessary, we are ready to provide more forces," he said in Delhi.
India's National Human Rights Commission also said it will investigate the causes of the violence.
More than 200 people have been arrested and 1,000 people detained in a crackdown that included state politicians, the Times of India said.
India's federal union government in New Delhi has called for an investigation into allegations of political involvement in fomenting the violence.
There have been allegations of political speeches inciting violence and unrest, the Indo-Asian News Service reported.
The official language of the city and district is Hindi, although the area is split nearly evenly between Hindus and Muslims.
The All India Council of Muslim Economic Upliftment, a non-government social service organization, estimates 49 percent of the 900,000 population are Hindus, followed by 47 percent Muslims and 7 percent Sikhs.
Uttar Pradesh Chief Minister Akhilesh Yadav alleged Monday that the riots in Muzaffarnagar were politically motivated, the Hindustan Times reported.
"The violence is a political conspiracy to defame and destabilize my [Samajwadi Party] government, which is doing a good job for the poor, youth, Muslims and all sections of society," Yadav said.
IANS quoted Union Home Minister Sushilkumar Shinde as saying Monday that the riots took place despite the central government warning Yadav about intelligence reports suggesting increasing tension in the state.
"I told [the] chief minister of Uttar Pradesh that tension is rising and you have to be alert," Shinde said. "[Yadav] said that he will make arrangements. However, this incident [the riots] has taken place."