ROME (Thomson Reuters Foundation) - A severe drought followed by floods has slashed agricultural production in Sri Lanka, leaving some 900,000 people facing food insecurity, the United Nations said, warning that without help the situation might further deteriorate.

Production of rice, the country's staple food, is forecast to drop almost 40 percent to 2.7 million tonnes in 2017, the U.N. Food and Agriculture Organization (FAO) and World Food Programme (WFP) said in a report on Thursday.

Other crops including pulses, chillies and onion are also expected to take a blow, it said.

Sri Lanka was hit by the worst drought in four decades last year, with poor rains continuing into 2017, causing many farmers to lose their crops and income, the agencies said.

In May, the situation was exacerbated by the worst torrential rains in 14 years, which triggered floods and landslides in the country's southwest, killing some 200 people and forcing many from their homes.

But in drought-affected areas in the north, rains were not sufficient to replenish reservoirs, and the second 2017 rice paddy harvest is expected to be at least 24 percent lower than last year's, said FAO official Cristina Coslet.

"The level of water in irrigation reservoirs is still well below the average," she told the Thomson Reuters Foundation by phone.

Some 225,000 households - or 900,000 people - face food insecurity, and have been forced to eat less and lower quality food, the report said.

Unable to grow their own crops, many families have to buy food at local markets where prices have spiked due to the crisis, it said.

FAO and WFP said seeds, equipment, irrigation support, and cash assistance are urgently needed to help farmers in the next planting season starting in September, and to prevent conditions from deteriorating.

"If (the planting season) fails the situation will worsen a lot for the families affected," Coslet said.

By Umberto Bacchi