Many people have been killed in clashes between Serbs and ethnic Albanians in Kosovo in what is seen as the worst violence in the UN-administered province since the war ended in 1999.
The BBC's south-east Europe analyst Gabriel Partos looks at what lays behind the latest events and where they might lead to.
Tensions are boiling over in many Kosovo towns
Q: What triggered the latest clashes?
Two incidents at the beginning of the week sparked off the violence that has engulfed many parts of Kosovo.
On Monday, a Serb youth was shot and serious injured in what is assumed to have been an ethnically-motivated attack in the village of Caglavica, near Pristina.
Local Serbs reacted by putting up roadblocks. In response, ethnic Albanians marched on the village and burnt some of the Serbs' homes.
Much more serious clashes further to the north, in the ethnically-divided town of Mitrovica, were prompted by the deaths of at least two Albanian boys who drowned on Tuesday after they had been reportedly chased into the river Ibar by Serb youths.
News of the Mitrovica riots appears to have led to violence in half-a-dozen locations across Kosovo - most of them involving attacks by ethnic Albanians on the minority Serbs.
Q: What is the background to the Kosovo clashes?
Kosovo has a long history of inter-ethnic enmity.
For Kosovo's ethnic Albanians things took a turn for the worse when the former Serb President, Slobodan Milosevic, in effect abolished what had previously been Kosovo's extensive autonomy in 1989.
After years of repressive direct rule from Belgrade, Kosovo Albanians started a guerrilla war in 1998.
A year later Nato intervened with the declared intention of preventing - and then reversing - a campaign of ethnic cleansing against ethnic Albanians.
Nato's 11-week series of air strikes led to the withdrawal of Serb security forces from Kosovo in June 1999.
The return of Kosovo Albanian refugees to their homes was accompanied by revenge killings against Serbs, many of whom then fled Kosovo.
Q: What is the current population balance between ethnic Albanians and Serbs?
In the absence of a post-war census, there are no official figures.
Estimates suggest that fewer than 100,000 Serbs - less than half the pre-war total - are left in Kosovo, out of a total population of about two million.
The rest are overwhelmingly ethnic Albanians - although there are also small communities of Roma, Muslim Slavs and Turks, some of whom have also suffered at the hands of Kosovo Albanian extremists.
Almost half the remaining Serbs live in and around Mitrovica - an ethnically divided town where Serbs are based in the northern districts and ethnic Albanians in the south.
There are pockets of Serbs in several enclaves in Kosovo, protected by the Nato-led K-For peacekeepers.
Q: Why did the violence erupt now - after a period of relative calm?
Inter-ethnic suspicions and hostilities have been simmering away.
In such a tense environment even one tragic incident - such as the drowning of the Albanian boys - can be like a spark that re-ignites the flames of ethnic violence.
Tensions tend to increase closer to the date of Nato's military intervention in Kosovo - 24 March marks the fifth anniversary of the alliance's first air strikes. The 1999 war brings back painful memories for both communities.
Besides, ethnic Albanians have been irritated by the recent remarks of the new Serbian Prime Minister, Vojislav Kostunica, who revived the idea of Kosovo's cantonisation - a plan ethnic Albanians regard as being tantamount to Kosovo's partitioning.
All this is taking place against the polarisation that comes with the preparations for Kosovo's second post-war parliamentary elections due in October.
Q: What are the chances of containing the violence?
There has been a steady, if unspectacular, improvement in the security environment in the last couple of years.
As a result, the strength of the K-For peacekeepers has been reduced from nearly 50,000 at the end of the war to 18,500.
The United Nations Administration in Kosovo (Unmik) may have thought that clashes between rival crowds - last seen two years ago - were a matter of history.
Now Nato has had to rush in reinforcements from Bosnia to beef up its presence.
On the one hand, there is a danger that violence breeds more violence.
However, the longer-term trend suggests that political struggle has increasingly been replacing the use of force, and there is a good chance that the K-For can, after a while, contain the violence, even if it has not been able to nip it in the bud.
Q: How long might Nato have to stay committed?
Nato's commitment remains open-ended. No-one expects a speedy settlement of the Kosovo issue.
And even if a negotiated solution is agreed - which at the earliest could be in three or four years - the Nato-led peacekeepers would need to stay to provide a safe environment for Kosovo's inhabitants - especially the Serbs - and guarantee the provisions of the settlement.
But, as in Bosnia, Nato is hoping to be able to cut its strength in Kosovo when conditions allow it.
Q: What does the future hold for Kosovo?
Though administered by Unmik - which has a veto over Kosovo's multi-ethnic self-governing institutions - Kosovo formally belongs to the union of Serbia and Montenegro.
In the long-term, Belgrade would like to reassert its control over the province.
But Kosovo's ethnic Albanians are adamant they want independence.
The UN's plan is to put standards before status - in other words to build a society with high standards of democracy, the rule of law and inter-ethnic tolerance before talks can get under way on determining Kosovo's future.
The UN envisages conducting a review around the middle of next year to assess what has been achieved by then.
If the review proves positive, talks on Kosovo's status could get underway in early 2006.
But if the latest violence persists, that tentative timetable is liable to be changed, and the entire process may take much longer.