Thousands of troops have been dispatched to restore peace in India's northern Uttar Pradesh state where 30 people were killed in Hindu-Muslim clashes, police said Monday.

Authorities declared a high-security alert following the violence triggered over the weekend during which mobs burned houses and a mosque in the state, which has been the scene of some of the nation's worst religious riots in recent decades.

Hundreds of troops were already patrolling in riot-hit areas as villagers crowded police stations seeking safety in Muzaffarnagar, 105 kilometres (65 miles) northeast of capital New Delhi, television footage showed.

Prime Minister Manmohan Singh condemned the violence and promised "all required assistance" to the state government for "tackling the situation".

"The number of those dead has risen to 30, we have also arrested 120 people," police spokesman Nityanand Rai told AFP by telephone, updating the previous toll of 28 after two men were killed in separate attacks on Monday.

Rai said contingents of army, riot police and federal troopers had been deployed in several districts including in worst-hit Muzaffarnagar, where 38 percent of the population is Muslim and the remainder mainly Hindu.

"The deployments in other places are a precaution against violence from spreading in the state. The situation is tense but calm," Rai said.

Junior Home Minister R.P.N. Singh said 5,000 extra paramilitary personnel were being rushed to violence-hit areas of the state, India's most populous with 200 million people.

"We don't feel safe in this village, where we form less than 10 percent of the population," Mohammed Haneef, a Muslim resident from Kharad village, 45 kilometres from Muzaffarnagar, told The Indian Express daily.

A journalist for the local IBN7 television network and a police photographer were among those killed in the violence, the most serious in recent years.

Politically pivotal Uttar Pradesh witnessed deadly riots in 1992 following the razing of a mosque by a Hindu mob. More than 2,000 people -- mostly Muslims -- were killed after the 16th-century mosque in Ayodhya was demolished in some of India's worst communal clashes.

The latest violence has triggered speculation that political parties are seeking to polarise the state along religious lines ahead of general elections due next year.

The state's secular ruling Samajwadi Party has accused the Hindu nationalist Bharatiya Janata Party (BJP) of fuelling tensions with inflammatory speeches.

A video posted online appearing to show two men being lynched by a mob seems to have aggravated tensions although police said it was faked.

The clashes erupted late Saturday after thousands of Hindu farmers held a meeting to demand justice over the killing of three Hindu men who had protested when a woman was allegedly harassed.

Provocative speeches calling for action against Muslims were allegedly made during the meeting.

The farmers were attacked as they were returning home, triggering an angry backlash, a senior police officer said.

Clashes then broke out in neighbouring villages between Hindus and Muslims and the army stepped in to try to control the situation.

"They started firing rounds at our homes from the fields and soon they were hurling petrol bombs," Muslim villager Iqbal Ansari told the Indian Express which showed a front-page photo of a bloodied child with a bandaged head in hospital.

"My house, my belongings and my life's savings were burned to the ground," he said.

A state BJP politician rejected accusations that the party was behind the violence.

"The government has failed on all the fronts... they are now searching for a scapegoat," Hukum Singh told NDTV.

Senior BJP leader Ravi Shankar Prasad accused the state government of failing to act in time to check the violence.

"The state government has failed miserably in maintaining communal harmony," Prasad told reporters in New Delhi.

The BJP is working to revive its fortunes before the elections by attacking the ruling Congress-led government over a string of corruption scandals.

The national government has warned that India is witnessing a rise in communal violence, and that there could be further such incidents in the run-up to polls.

"Communal violence incidents have increased since last year. While 410 incidents occurred in the country last year, this year, till now, 451 incidents have taken place," federal Home Minister Sushilkumar Shinde said.