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Armed groups deployed in the suburbs of on Tuesday, sparking security fears ahead of an expected delay of , as three key candidates met in the country's east.

Images posted online in the morning showed a tank and pickup trucks mounted with machine guns in , where armed men guarding sandbags blocked some roads.

Schools and the University of Tripoli closed as a precaution but there were no firefights, residents said.

The mobilisations came as Libyans await an official announcement that presidential elections, set for Friday, have been postponed.

The vote is meant to cap a United Nations-led peace process aiming to move the oil-rich North African country past a decade of conflict since the country's 2011 revolt.

But divisions over the election's legal basis and the candidacies of divisive figures have undermined the process.

While no party has officially announced the polls will be delayed, such a move is widely viewed as a foregone conclusion, partly due to the difficulty of holding a free and fair vote given the fragile security situation.

On Tuesday, two leading presidential candidates from western Libya, ex-interior minister Fathi Bashagha and former deputy prime minister Ahmed Maiteeq, met in Benghazi with eastern warlord Khalifa Haftar, who is also seeking the presidency.

The content of their talks was not disclosed, but an adviser to Bashagha told AFP that the reason for the visit was to "break down obstacles... and show that it is possible to unite".

'Risk of clashes'

In the afternoon, roads in Tripoli that had been closed were reopened and fewer gunmen were on the streets, an AFP correspondent said.

Jamila Rizgalla, a professor at the university, told AFP that "teachers, staff and students were asked to evacuate the campus and leave immediately. Lectures were interrupted and the university was closed due to security tensions" in the nearby Ain Zara and Fornaj districts.

Libya's Tripoli-based unity government, which took power in March with a mandate to take the country to elections, did not immediately comment on the developments.

Armed groups had also deployed in Tripoli's streets last week after the unity government dismissed Abdulbasit Marwan, a senior military official backed by several of Tripoli's powerful armed groups.

The United Nations' Libya mission UNSMIL voiced concern over the armed deployments, warning such mobilisation "creates tensions and increases the risk of clashes that could spiral into conflict."

In a statement, it called for the resolution of any disagreements through dialogue, "particularly at this stage when the country is navigating through a difficult and complex electoral process that should usher in a peaceful transition."

The Libyan capital is under the control of an array of armed groups affiliated with the defence and interior ministries.

The country has seen a decade of violence since the 2011 NATO-backed uprising that overthrew and killed dictator Muammar Gaddafi.

Myriad armed groups, foreign forces and mercenaries have filled the void.

Libya has been relatively calm since a landmark ceasefire between eastern and western camps in October last year, but despite high hopes for peace the UN has struggled to overcome the country's deep, complex divisions.