NEW DELHI: India's prime minister assured migrants from the northeast of the country that they were safe as thousands continued to flee from Mumbai, Bangalore and other cities on Friday, fearing a backlash from violence against Muslims in Assam state.

Railway authorities have laid on extra trains from Bangalore and other cities this week for the two-day journey back to Assam in the northeast. Some media reports said that by Friday as many as 15,000 people had left cities in the south and west, including Mumbai and Pune.

“What is at stake is the unity of our country. What is at stake is communal harmony,” Prime Minister Manmohan Singh told parliament.

“I assure you ... that we will do our utmost to ensure that our friends and our children and our citizens from the northeast feel secure in any and every part of our country.”

Muslims across India have been alarmed by clashes in recent weeks between indigenous people in the northeastern state of Assam and Muslim settlers from neighbouring Bangladesh.

About 75 people have been killed and more than 400,000 displaced.

Two people were killed and dozens were wounded last week when about 10,000 people rioted in the city of Mumbai following a protest by Muslims against the violence in the northeast.

Rumours of revenge attacks by Muslims have been swirling, many of which have been carried on social media and mass mobile phone text messages.

“It is the obligation of all of us, regardless of the party, that we work together to create an atmosphere where this rumour-mongering will come to an end,” Singh said.

The Assam violence angered India's Muslims, who represent about one-fifth of the population, and raised tensions in a country where religious and ethnic divisions have simmered for decades, occasionally erupting into communal blood-letting.

India's 1.2 billion people are predominantly Hindu.

Analysts have accused political parties and religious organisations of exploiting ethnic tension for their ends.

The Hindu nationalist opposition Bharatiya Janata Party (BJP), which has in the past been accused of fomenting Hindu-Muslim violence, blames the Assam riots on uncontrolled immigration into the state from Muslim-majority Bangladesh.

It says the Congress party, which leads the coalition running the federal government, allows immigration to win votes from new arrivals.

Hundreds of thousands of people from the poverty-plagued northeast live in the south and west of the country, studying in colleges or working in industries such as construction, restaurants, hotels and security. Media reports said that in Bangalore alone there are about quarter of a million.

Interior ministry officials declined to put a number on the exodus, but in just one city - Pune in the west - railway officials said that at least 3,000 more than usual had taken trains to Kolkata, gateway to the northeast, since Monday.