High school students in Eswatini, Africa's last absolute monarchy formerly known as Swaziland, have been boycotting classes and staging low-key protests for the past month.

They are mainly calling for the release of two lawmakers arrested during pro-democracy protests earlier this year.

The army has been "deployed across the schools to intimidate, but that has not deterred the students," Lucky Lukhele, spokesman for the pro-democracy Swaziland Solidarity Network, told AFP.

"But today it was reinforced," he added, claiming that 17 students, including a seven-year old, were arrested during Monday's protests.

Army spokeswoman Tengetile Khumalo confirmed the deployment.

"The army is not an enemy of the people and deploying them in schools doesn't mean there is war but just an assistance to the other forces to maintain order," she said.

Mduduzi Gina, general secretary of the Trade Union Congress of Eswatini, said "the pupils are calling for political reforms".

"Having the army... and cops deployed in the schools will worsen the situation in Eswatini," he warned.

Civil society and opposition groups demonstrated in the capitals Manzini and Mbabane in June, looting shops and ransacking properties, some of which belonged to King Mswati III.

At least 27 people died as police clashed with protesters in some of the worst unrest in the southern African country's history.