Former Brazilian President Jair Bolsonaro underwent intestinal surgery in Brasilia on Sunday after being hospitalized with "unbearable" abdominal pain on Friday.

In a statement, the private DF Star hospital in the Brazilian capital said the 70-year-old underwent a laparotomy, involving an incision through the abdominal wall, "to treat intestinal adhesions."

The surgery began at 8:30 a.m. local time (1230 CET) and was expected to last six hours, a source close to Bolsonaro's entourage told the AFP news agency.

Earlier this weekend, doctors had said the pain was caused by complications linked to a knife attack during his presidential campaign in 2018. The stabbing was nearly fatal, as he lost some 40% of his blood and had to have emergency surgery.

The far-right populist had himself said on social media that the issue was "a consequence of the multiple surgeries I needed to undergo after the attack in 2018."

Bolsonaro was initially hospitalized with severe abdominal pain while touring Rio Grande do Norte in northeastern Brazil on Friday - an impoverished region and historically a leftist stronghold.

Doctors in the city of Natal initially told the media that he was stable and did not need emergency surgery before transferring him to Brasilia on board a medical aircraft.

"After so many similar episodes over the past few years, I had gotten used to the pain and discomfort. But this time, even the doctors were surprised," Bolsonaro said in a social media post on Saturday. He underwent several surgeries during his presidency from 2019-2022.

Staff in the capital, however, said that "new tests revealed the persistence of the intestinal blockage despite the clinical treatment initially adopted" and "opted, by common agreement, for the surgical intervention."

Bolsonaro has been on a tour around Brazil to push for an amnesty bill for his supporters who stormed the capital after his 2022 election loss. 

Last month, Brazil's Supreme Court ruled he will stand trial for allegedly plotting to overthrow the legally elected government.

He denies the charges, calling the case a politically motivated attack.

Meanwhile, the far-right politician has been trying to posture himself as a leading candidate in the elections next year even though he has been barred from holding office until 2030 for making unsubstantiated claims of fraud in Brazil's electronic voting system.

Edited by: Wesley Dockery