Sri Lanka's jailed former president was rushed to intensive care at a state hospital on Saturday, a day after being charged with misusing government funds for foreign travel.

Ranil Wickremesinghe, who was remanded in custody on Friday night, was severely dehydrated and required close monitoring, said the deputy director-general of Colombo National Hospital.

"He has to be closely observed and treated for acute dehydration to prevent serious complications," Rukshan Bellana said.

"He was a severe diabetic with high blood pressure when he was brought in."

Opposition legislators who visited 76-year-old Wickremesinghe in prison earlier in the day reported that he had been in good spirits.

Opposition parties have accused the government of jailing him over fears he could return to power.

Wickremesinghe lost the last presidential election in September to Anura Kumara Dissanayake, but has remained politically active despite holding no elected position.

He was arrested on Friday as part of Dissanayake's campaign against endemic corruption in the island nation, which is emerging from its worst economic meltdown in 2022.

Wickremesinghe stands accused of using state funds to finance a private visit to Britain in September 2023, while returning from attending the G77 summit in Havana and the UN General Assembly in New York.

His two-day UK visit was to participate in the conferring of an honorary professorship on his wife, Maithree, by the University of Wolverhampton. He maintained that his wife's travel expenses were met by her and that no state funds were used.

The offences carry a maximum of 20 years in jail and a fine not exceeding three times the value of the misappropriated funds estimated at 16.6 million rupees (US$55,000). (AFP)