MUMBAI (Reuters) - Farmers on Wednesday stepped up their agitation in Madhya Pradesh after six were shot dead in clashes the previous day, forcing the authorities to impose a curfew in some areas.

The outburst of discontent in India’s heartland farming states of Madhya Pradesh and neighbouring Maharashtra poses a challenge for Prime Minister Narendra Modi, who has promised to double farmers’ incomes over the next five years.

Farmers’ leaders say the six were shot dead by police during a protest in the central city of Mandsaur, a version questioned by the state government which has ordered an investigation.

“We will continue our protest until the government accepts our demands,” said Sunil Gaur of the Rashtriya Kisan Mazdoor Sangh, or National Farm Workers’ Union, which called Wednesday’s state-wide shutdown.

“The government has complicated the situation by killing six innocent farmers.”

Farmers dumped vegetables and milk on the roads when the strike kicked off last week, demanding billions of dollars in debt forgiveness and better prices for their produce.

Tension persisted in some parts of Madhya Pradesh, with a curfew imposed throughout the district of Mandsaur where the farmers died, a police officer said.

“The curfew won’t be lifted until the situation becomes normal,” said the officer, D. Kavita.

Madhya Pradesh Chief Minister Shivraj Singh Chauhan appealed to farmers to keep the peace and accused the opposition Congress party of being behind violence that broke out at the protests.

“The government is with the farmers,” he told television news agency ANI, a Reuters affiliate. “Some people want to ruin the atmosphere. Stay away from such people.”

Congress Vice-President Rahul Gandhi was expected to visit Mandsaur on Wednesday. “This government is at war with the farmers of our country,” he said on social network Twitter.

In the past, ruling parties have lost elections in the eastern state of West Bengal, western Maharashtra and the northern state of Uttar Pradesh after farmers died at the hands of security forces.

The Maharashtra farmers’ strike entered its seventh day, despite an assurance from Chief Minister Devendra Fadnavis that the state would waive distressed farmers’ debts before Oct. 31.

The prices of fresh produce have more than doubled in cities such as Mumbai, India’s main financial centre and the capital of Maharashtra.

Two-thirds of India’s population of 1.3 billion depend on farming for their livelihood, but the sector makes up just 14 percent of gross domestic product, reflecting a growing divide between the countryside and increasingly well-off cities.