Eswatini’s main opposition leader has been poisoned as part of an assassination attempt and is being treated in hospital, his party says.

Mlungisi Makhanya, 46, has been living in exile in neighbouring South Africa for the last two years, saying he fears for his life at home following a violent crackdown on pro-democracy activists in Africa's last remaining absolute monarchy.

"Our president has been stabilised but he is still in a critical condition," the People’s United Democratic Movement (Pudemo) said.

Eswatini spokesman Alpheous Nxumalo denied state involvement, saying the "government does not kill or poison suspects".

Pudemo says the attempt on its leader’s life comes ahead of planned protests next month calling for multi-party elections.

The country, formerly known as Swaziland, allows independent candidates to stand for parliament but does not allow political parties to participate.

King Mswati III has been on the throne since 1986 and rules by decree. He has been criticised for his extravagant lifestyle and is regularly accused of not allowing any dissent, which his government denies.

Last year, Thulani Rudolf Maseko, a human rights lawyer, who was opposed to the king, was killed in his home in the capital, Mbabane, sparking widespread condemnation.

In September 2022, Makhanya’s home in Eswatini was set alight in an alleged firebomb attack by state agents. He now lives in South Africa’s capital, Pretoria, with his family.

Makhanya leads Pudemo, one of the leading pro-democracy parties which are theoretically allowed, but banned from participating in elections.

He was allegedly poisoned in the early hours of Tuesday inside his house in Pretoria by an unnamed "young boy", who Pudemo said was used as an "agent of evil intent by Swazi government".

Makwanya was rushed to a Pretoria hospital escorted by the South African police, the Swaziland News website reported. He was later moved to the Intensive Care Unit (ICU), in a critical but stable condition, it added.

He reportedly informed police and doctors that he had been poisoned and robbed of his cell phones.

In a press briefing on Wednesday, Wandile Dludlu, the Pudemo deputy president, said an "extremely dangerous and fatal" pesticide poison was used in the incident.

"It is encouraging that the president has survived a day," Dludlu added.

"It was an assassination attempt on the life of our leader."

This was rejected by the Eswatini government.

"Government, through the law enforcement agencies - that adheres to a strict code of ethics and professionalism - only apprehend suspects and bring them to Justice, and they are brought to justice 'alive', not 'dead'," Nxumalo said in a statement.

The Pudemo party has appealed for international support to ensure Makhanya's security and that of his family while in hospital.

The Swaziland Solidarity Network (SSN), a group of Swazis living in South Africa, condemned what it termed a "bold attack" and a "clear assassination attempt" against Makhanya.

It called on the South African government to take action against Swazi state agents it said were targeting exiled pro-democracy activists "fighting for freedom" .

Opposition parties have accused security agents of killing dozens of protesters who have blamed the lack of development in the country on the current political system.

In 2021, student-led protests that began over alleged police brutality morphed into calls for political change. At least 46 people died in a series of clashes between the security forces and demonstrators, according to Human Rights Watch.

The government has disputed this figure and said that the police were responding to violent attacks.

"This is a political fight between the oppressed masses and the traditional autocratic monarch," Dludlu said, vowing that Pudemo would proceed with next month's protests as planned.