At midday the streets of Liberia's capital bustle with life, a thousand raised voices drowned out by motorbike horns and the air thick with the aroma of boiled casava and palm butter.

Further out, empty buildings peppered with bullet holes bear silent witness to an all too recent trauma, their crumbling facades disfigured by charred window frames resembling hollow, dead eyes looking out at Monrovia.

Liberia is entering its second decade of fragile peace after one of the bloodiest civil wars in African history, yet the spectre of renewed conflict haunts the battle-scarred streets of its shattered capital.

At his desk in a squalid office in downtown Monrovia, Liberia's wartime rebel leader Sekou Damateh Conneh warns of growing discontent among his former fighters.

"If I were a troublemaker we would have trouble here every day because, as combatants who are ready for trouble, they are talking to me every day," says the onetime head of the disbanded Liberians United for Reconciliation and Democracy (LURD).

"They are ready," Conneh warned.

"They don't have money and they are frustrated. They can do anything. I tell them no, we can't do that now, we need peace in this country. People have suffered in this country a lot."

Deep psychological and physical scars persist after two back-to-back civil wars that ran from 1989 to 2003 and claimed a quarter of a million lives.

Numerous rebel factions raped, maimed and killed civilians, some making use of drugged child soldiers, and deep ethnic rivalries and bitterness remain across the country of 4.2 million.

In June 2003, LURD laid siege to Monrovia, deposing warlord president Charles Taylor after several bloody battles in which fighters were accused of firing mortar shells into civilian areas, killing dozens.

Taylor bowed to pressure to go into exile and is serving a 50-year sentence in a British jail for arming rebels during neighbouring Sierra Leone's civil war, which claimed 120,000 lives.

Since 2004, the United Nations has disarmed some 100,000 Liberian fighters, providing each with $300 (219 euros) and promises of free education and training -- which opposition politicians say were never kept.

In the bleak economy of post-war Liberia, thousands of experienced killers are suffering ill health and drug addiction, but have no access to welfare.

"There are a lot of people who, as combatants, there are no jobs for them, no programmes for them. Everybody is abandoned," Conneh said.

Humanitarian and security organisations regard such people as a regional threat, noting that many were recruited as mercenaries by Ivory Coast's ex-president Laurent Gbagbo in the 2010-11 crisis, when he sought to cling to power after an electoral defeat.

Unlike other countries in the wake of conflict, Liberia did not absorb former combatants into the security forces and instead laid off more than 14,000 soldiers.

"This ... constitutes a relatively large number of unemployed and highly disgruntled individuals who feel disadvantaged," ACCORD, a South African NGO specialising in conflict resolution, said in a 2013 report.

"The fact that the majority of these former combatants are idle means that the chances that they can be mobilised and used to destabilise other countries in the region... is high."

Liberia's Ellen Johnson Sirleaf, a Harvard-trained former World Bank employee, made history in 2005 when she became Africa's first elected female president.

Feted in the West as a visionary leader who brought massive investment and a measure of stability to a nation ruled by guns for so long, opinion of "Ma Ellen" at home is more nuanced.

She faces criticism for alleged nepotism and corruption in a country with an unemployment rate of about 80 percent and which lacks basics such as water and reliable electricity.

Sirleaf was forced to apologise to Liberia's Truth and Reconciliation Commission for her previous support of Taylor, having once helped finance his rebels. The commission ruled that Sirleaf should be banned from holding political office for 30 years, although Liberia's parliament is unlikely to ever uphold the decision.

During her tenure the United Nations Mission in Liberia (UNMIL) has been the guarantor of security but it is reducing its troop deployment from a height of 15,000 to just 3,750 by next summer.

Responsibility for law enforcement is in the hands of an underfunded, demoralised police force deemed by Liberians to be the most corrupt institution in the country, according to a 2013 study by Transparency International.

The security situation in Liberia is "stable" but fragile, according to UNMIL, which has pointed to a worrying rise in vigilante activity, often by disgruntled, poorly paid workers in mining towns.

"Some Liberians call it 'mob justice'. We do not call it mob justice because that is not an acceptable form of justice, where people are hunted down sometimes on the basis of rumours alone and hurt or killed by communities," UNMIL head Karin Landgren said in a recent briefing to journalists.

Critics concede, however, that Sirleaf's management of the transition to peace has not been an unmitigated failure.

The first of a network of five "justice and security hubs" with a courthouse, police, human rights monitors and immigration officers has been set up in the central town of Gbarnga.

The launch is seen as an important step in the decentralisation of government services and is also hugely symbolic of Liberia's post-war progress, since Gbarnga was once the base of Taylor's rebellion.

In a smart move to win hearts and minds, she has also appointed longtime rival George Weah, a footballing legend who garners respect on all sides, as "peace ambassador" and head of the government's peace and reconciliation committee.

"A lot of people are bitter in this country. But they are human beings like us. We need to talk to them," Weah told AFP at his party headquarters at the southeastern edge of Monrovia.

"Things that we did before, we need to drive away from those things and encourage (people) by integrating them into society and letting them know that there is hope and that they need help."