NEW DELHI, Feb. 13 (Reuters) - Police in India on Tuesday fired tear gas at hundreds of farmers and their supporters who were marching to New Delhi to pressure the government to honour a 2021 promise to pay them more for crops.

Security in the capital was tightened after farm unions from northern breadbasket states called for protests a day after talks with ministers aimed at securing minimum prices for a range of crops failed.

At midday, police fired teargas to disperse marchers at Shambhu, a border crossing between Punjab and Haryana states, about 230 km (143 miles) north of Delhi and where many had joined the march.

The march is latest in a series of similar protests which began more than two years ago and comes months ahead of national elections in which Prime Minister Narendra Modi will seek a third term, with farmers forming an influential voting bloc.

Farm unions are seeking guarantees, backed by law, to provide more state support or buy crops at a minimum price. They also want the government to honour a promise to double their income.

"The government has not been able to make a strong decision on anything... We thought that giving time is not suitable now," Sarwan Singh Pandher, the general secretary of Punjab Kisan Mazdoor Sangharsh Committee (KMSC), told ANI news agency.

Agriculture Minister Arjun Munda told reporters after talks with union leaders that some issues had been resolved but more discussions were needed.

"Any problem can be solved with discussion. We are hopeful that we will bring solutions," he said.

Police have prohibited large gatherings in New Delhi and blocked sections of major routes leading to the capital from Punjab.

The government announces minimum prices for more than 20 crops each year, but state agencies buy only rice and wheat at these prices, which benefits only about 6% of farmers.

In 2021, when Modi's administration repealed the farm laws after the farmers protested, the government said it would set up a panel to find ways to ensure support prices for all farm produce.