Police in eSwatini fired teargas and water canons on Wednesday at thousands of civil servants protesting against low pay and rising living costs in Africa's last absolute monarchy.
Teachers and workers went on strike last week in the four main towns of eSwatini -- a tiny southern African kingdom until recently known as Swaziland and entirely surrounded by South Africa.
They accused King Mswati III of failing to provide sufficient wages, and flocked to the capital Mbabane on Friday to discuss action with opposition pro-democracy groups.
Frustrations boiled over into a series of protests around the country this week.
More than 3,500 people marched in Mbabane and the neighbouring city of Manzini on Monday, and around 3,000 protesters showed up in the capital again on Wednesday.
"Today we mean serious business," said Mbongwa Dlamini, head of the Swaziland National Association of Teachers.
An AFP reporter on the scene said police intervened when the crowd diverged from their authorised protest route.
South Africa's trade union federation announced "border protest action" in the neighbouring province of Mpumalanga on Wednesday "in support" of the eSwatini strike.
"The workers demand only 7.8 percent salary adjustment while the Mswati regime spends millions of rands for his lavish lifestyle," said the Congress of South African Trade Unions (COSATU) in a statement.
Wandile Dludlu, national coordinator of an eSwatini pro-democracy coalition, welcomed COSATU's support.
"This is (a) fight against both economic and social justice," said Dludlu. "Protest action is not like a coffee session."
The government said earlier this month that it was unable to meet the protesters' demands.
"Government is in a challenging financial situation, hence (its) inability to award civil servants with a cost of living adjustment for the past two years," Prime Minister Ambrose Dlamini said in a statement.
King Mswati III was crowned in 1986, when he was just 18. He has come under fire for his expensive tastes, frivolous spending and prioritising his family's needs.
The king's older daughter Princess Sikhanyiso was appointed as a member of cabinet last year, stoking outrage among pro-democracy groups.
"She only goes to parliament when she has to collect her fat cheque," Dludlu told AFP last week.