Ex-general Khalifa Haftar has garnered growing support amid frustration at the lawlessness in Libya three years after the overthrow of dictator Moamer Kadhafi.
"Yes to dignity," read banners carried by demonstrators at Martyrs' Square in Tripoli.
Thousands more pro-Haftar demonstrators gathered outside Tibesti Hotel in the eastern city of Benghazi, a stronghold of the Islamists, and in Baida, further east.
"Yes to the army, yes to the police," their banners read. "No to militias, Libya will not become another Afghanistan."
His forces launched an assault against jihadists on May 16 in the Mediterranean city of Benghazi, birthplace of the 2011 uprising against Kadhafi, in which at least 79 people were reported killed.
That prompted the government to brand him an outlaw and claim he was attempting a coup.
But Haftar insists he has no interest in power, just an end to the Islamist-dominated General National Congress (GNC), or interim parliament.
On Sunday, forces that support Haftar attacked and set fire to part of the GNC building in Tripoli.
Voicing alarm over the chaos and violence a month before elections, Western powers today issued a joint appeal for a peaceful transition in the North African nation.
Britain, France and the United States -- the three powers who led the NATO-backed attacks that ousted Kadhafi -- urged a "peaceful and democratic" transition, in a statement also signed by Germany, Italy and the EU.
The Western powers, "deeply concerned by the repeated acts of violence, call on all sides to refrain from the use of force and to address differences by political means", it read.
The Libyan government yesterday urged militias to withdraw from the capital after the embattled GNC had sought help from ex-rebel fighters.
But calm returned today after dignitaries from two rival regions -- supportive and opposing the GNC -- brokered a compromise to prevent armed clashes in Tripoli.
