Security forces were on high alert across Libya on Sunday as the North African nation marked two years since the start of the revolt that toppled Muammar Gadhafi.

Borders have been closed and some international flights suspended amid fears of a new outbreak of violence.

A child waves a Libyan flag, ahead of the second anniversary of the Feb 17 uprising, in Benghazi, on Saturday. Esam Al-Fetori / Reuters

The anniversary of the uprising that ended with Gadhafi's killing in October 2011 comes as Libya's new rulers battle critics calling for a "new revolution" and accusing them of failing to usher in much needed reforms.

On Friday, thousands of people gathered in the main cities of Tripoli and Benghazi to celebrate the initial Feb 15, 2011 protest that ignited the revolt two days later.

There is no official program for Sunday's anniversary, but the authorities have taken steps aimed at preventing any violence on a day when spontaneous celebrations are expected.

Tahrir Square in Benghazi was set to be the focus of the celebration, attended by national assembly president Mohammed Megaryef, the de facto head of state, and members of the government.

Libya's borders with Egypt and Tunisia were closed from Thursday for four days, and all international flights have been suspended except at the airports of Tripoli and second city Benghazi - the cradle of the "Feb 17 revolution".

Prime Minister Ali Zeidan said the measures were taken to avoid "any bid to undermine Libya's security and disrupt celebrations marking the anniversary of the revolution".

Checkpoints have also been set up across Benghazi and Tripoli.

"The joy that motivated people in towns and villages on Friday and Saturday has allowed Libyans to prove to the world that they are a civilized people who revolted against injustice and tyranny to gain freedom," Zeidan said.

Opposition groups are demanding that former Gadhafi government officials be barred from holding public office, and a leaflet circulated in Tripoli calls for a "popular revolt" and civil disobedience to bring down the current government.

It is unclear who is behind the leaflet and the calls for protests, but Libyan officials and several organizations, including Islamic groups, accuse remnants of the former ruler of fomenting protests to, "sow disorder and instability".

Resentment of Tripoli

The mood was mixed between those happily waving flags and singing the national anthem, their faces painted with the Libyan flags, and others standing soberly watching.

"I am not celebrating, I am not carrying a flag," said Ahmed al-Mijbari as fireworks exploded over his head. "I am here stranding for my right, for the east and to put a stop to centralization."

A few meters away, Iman Bugaighis, a professor at the University of Benghazi, was out to celebrate.

"I was worried something may happen today," she said. "But I am here to show my happiness at our revolution and celebrate with my people."

Many Libyans, particularly those in the east, have been urging citizens to take to the streets to voice their discontent over the Tripoli government's inability to provide security by disarming militias or moving toward writing a constitution.

In Benghazi, daily life has been disrupted by violence and unrest on top of demands for greater autonomy or investment in a region 1,000 km east of Tripoli.

There are calls in the region - where most of Libya's oil wealth lies - for a return to a federal political structure and more regional autonomy, which Libya had before Gadhafi seized power in a coup in 1969.

AFP-Reuters