The violation comes days after the Presidential Council of the internationally-recognised Libyan government and the Tobruk-based so-called House of Representatives, which supports warlord Haftar, agreed to an immediate cease-fire.
Militias aligned with warlord Khalifa Haftar have violated a recently declared ceasefire, according to the Libyan army.
"The terrorist al Karama gangs and the Russian Wagner group affiliated with them attempted to target our valiant forces with more than 12 Grad missiles," the government said in a statement on Facebook on Thursday.
The army said it was "a clear breach of the cease-fire agreement that was announced last Friday," stressing that "the operation of Sirte and Jufra will not hesitate to respond to these actions, as approved by the field operations."
Earlier on Thursday, the Libyan government warned Haftar against continuing attacks and crimes in the cities of Sirte, in the north of the country and Taraghin in its central region.
On August 21, the Presidential Council of the internationally-recognised Libyan government and the Tobruk-based so-called House of Representatives, which supports warlord Haftar, agreed to an immediate cease-fire. Their two statements met on common points, most notably the truce and holding of presidential and parliamentary elections.
The agreement was widely welcomed by the international community and particularly Arab countries, while Haftar's militia rejected it.
Libya's Prime Minister Fayez Al Sarraj declared his readiness to implement any agreement that meets the acceptance and consensus of all Libyan actors and called on Libyan protesters not to be dragged into the calls for sabotage over the deterioration of living conditions, saying: "I have ordered all state agencies to protect the peaceful demonstrators."
He warned that gunmen were infiltrating the peaceful protests to carry out acts of sabotage and riots in order to bring down the prestige of the Libyan state.
Al Sarraj also thanked Turkey, saying that it "stood with the Libyans at a time when many abandoned us."
'Gang of thugs'
Libya's government on Thursday warned it would use force against militia gunmen who broke up peaceful protests by firing at crowds the day before.
Demonstrations began on Sunday in the capital Tripoli against poor public services and living conditions.
While police have monitored the protests, gunmen on Wednesday attacked a peaceful demonstration by "firing live ammunition indiscriminately," said Fathi Bashagha, the GNA interior minister.
The gunmen also kidnapped demonstrators, "sowing panic among the population and threatening security and public order," Bashagha said.
He promised to "protect unarmed civilians from the brutality of a gang of thugs" and said he was ready to use force to do so.