International concerns are growing about Bosnia’s fragile peace.

The UN Security Council has received a stark briefing about an "existential threat" to the country, while G7 foreign ministers condemned moves by the Serb autonomous regions towards secession.

Colonel Colm Doyle, who was head of the European observer mission in the Bosnian capital Sarajevo during the 1992-5 war and recorded his experiences in his book 'Witness to War Crimes’, said the situation should be taken "very seriously".

"I think it could take just one act," he told RTÉ News. "Certainly when I was working there in the early '90s, I was struck by how fast things could be torn asunder."

What's the background?

Bosnia suffered the worst atrocities in Europe since World War II during its 1992-5 civil war. Over 100,000 people died and a further two million were displaced in the conflict before a NATO intervention, followed by an imperfect US-brokered peace deal - the Dayton Agreement - brought hostilities to an end.

The Dayton Accords divided Bosnia along ethnic lines into two self-governing regions.

Croats - who are mainly Roman Catholics - and Bosniaks - who are mainly Muslim - are the majority population in the Federation of Bosnia and Herzegovina. In the separate enclave of Republika Srpska, the mainly Serbian Orthodox Serbs are the majority population.

Dayton set up a rotating three-member presidency made up of a Bosniak, a Croat and a Serb.

The international community also appointed a High Representative with wide-ranging powers to oversee the implementation of the accords. The current office holder is Christian Schmidt, a German diplomat.

Last week, an overwhelming majority in the Republika Srpska regional assembly voted to withdraw from the institutions set up under Dayton and set up its own army, tax, customs and policing structures - a move that would bring it into conflict with Federation security forces.

Colonel Colm Doyle, former head of the European observer mission in Sarajevo

Why did Republika Srpska take this step now?

The past looms large over this latest crisis. Republika Srpska has been consistently unhappy with the Dayton arrangements, but the latest crisis was triggered in July.

Before the previous High Representative left office, he used his wide-ranging powers to impose a law aimed at stamping out genocide denial in Bosnia.

Valentin Inzko set out criminal penalties for naming awards or public places after persons convicted of genocide; incitement to hatred on ethnic grounds or denial of genocide where it has been described as such in a court ruling.

The 1995 massacre of over 8,000 Muslim Bosniak men and boys by Bosnian Serb forces at Srebrenica is the most infamous example of this, but many Serbs dispute international court rulings and the description of the mass murder as genocide.

The leader of Republika Srpska, Milorad Dodik, seized the opportunity offered by the High Representative’s move to announce he would cease applying most laws introduced by all high representatives and withdraw from national military, policing and tax institutions and set up parallel structures in Republika Srpska.

Of particular concern are Mr Dodik’s plans to form a Bosnian Serb army, which his opponents within the autonomous territory have called "delusional" and "dangerous".

Even before the vote, the High Representative described the plans as "tantamount to secession without proclaiming it".

Scandals over the Dodik government's handling of the Covid-19 crisis caused its secessionist rhetoric to rise just as its popularity slumped.

Milorad Dodik is the leader of Republika Srpska

Who is concerned by these steps?

The UN, the EU, the US and regional governments have all condemned Mr Dodik's moves.

"Bosnia and Herzegovina is facing the greatest existential threat of the post-war period," the UN Security Council heard last month in a report from the High Representative for the Implementation of the Peace Agreement.

The most pressing issue, according to Christian Schmidt, is the threat by the country's Serb autonomous region, Republika Srpska, to withdraw from Bosnia.

The International Crisis Group - an NGO which supports conflict resolution - said in a recent report that the country's "viability as a state" is in jeopardy due to Serb threats of secession and a Croat boycott of elections.

"Bosnia looks set to disintegrate politically within the next 18 months or so, potentially leaving in its wake a breakaway Republika Srpska that is unlikely to win international recognition and the remnants of the Federation paralysed by Bosniak-Croat feuds," Crisis Group warned in a November paper by analysts Marko Prelec and Ashish Pradhan.

"I remember speaking with the head of the Jewish community in Sarajevo when I was working there in 1992, and he said to me 'It only takes the bodies of two people to be seen in the streets of Sarajevo and this place will explode'," Colonel Doyle told RTÉ.

Sarajevo city is the capital of Bosnia and Herzegovina

Who supports the moves?

While Serbia might welcome union with Republika Srpska at some future point, jeopardising its economic and political relations with the EU and US and risking sanctions by supporting a breakaway state with little or no international recognition is also a serious consideration.

Mr Dodik also claims to have the support of "friends" who would help in the event of force being used.

He met with Russia's foreign minister in Belgrade in October. While Moscow has been publicly critical of the Office of the High Representative, it has not explicitly supported the latest moves towards secession by Republika Srpska.

Is this the only problem?

No. Among other things, there are divisions over the electoral system between Croats and Bosniaks in the Federation of Bosnia and Herzegovina, which has meant no new government has been appointed in the region since 2018.

Women mourn as 19 victims of the Srebrenica genocide were buried earlier this year after their remains were identified

What can be done?

Crisis Group recommends the US and EU make efforts to unite Croats and Bosniaks. To counter the threat of secession it says "a robust response" is required.

Clear consequences should be laid out for separatist action. At the same time, considering what concessions could be made to Republika Srpska within the Dayton framework might offer the scope to halt moves towards secession.

An EU peacekeeping mission is already deployed in Bosnia, but it is not at the scale required to deal with a major crisis, Colm Doyle believes.

He noted: "The international community is represented inside in Bosnia with a small 700 strong European Union-led stabilisation force, but 700 troops, you know, in a country like Bosnia is really very small."