Ukraine crisis: Will war return?
Pro-Russian rebels control broad swathes of eastern Ukraine and a fragile ceasefire with government forces could end at any time and return the region to deadly conflict.
Ukraine's Western allies accuse Russia of sending in troops and armour to help the rebels - an allegation repeatedly denied by the government in Moscow.
Some 4,000 people have already lost their lives in a crisis that few saw coming.Why is eastern Ukraine on the verge of full-scale conflict again?
Fighting started in April and raged for months until Ukraine and the separatists came to a deal to halt the violence and free prisoners.
However, although the intensity of the conflict subsided, the clashes never really ended. A battle for control of Donetsk airport, currently in Ukrainian hands, has raged throughout.
When the rebels held their own local elections on 2 November, in defiance of the government in Kiev, both sides accused each other of tearing up the peace deal and a new surge of violence erupted.Why did the fighting start?
In April, pro-Russian activists seized control of government buildings in towns and cities across the Donetsk and Luhansk regions.
The events were a repeat of what had happened in Ukraine's Black Sea peninsula of Crimea.
Gunmen there seized government buildings in February and raised the Russian flag a week after elected President Viktor Yanukovych, friendly to Moscow, was toppled after massive pro-European Union street protests.
Russian politicians and media portrayed the Kiev leaders as Ukrainian nationalists bent on violating Russian-speakers' rights.
A flawed referendum on joining Russia was quickly held in Crimea and within a month the peninsula's annexation was complete.
There was little bloodshed in Crimea but Ukraine's fledgling revolutionary government was in no position to fight back, with only 6,000 troops reportedly ready for combat.
However, when pro-Russian separatists made a move on Ukraine's industrial east and Russian forces appeared to be building up on the borders, the Kiev authorities ordered an "anti-terrorist operation".What was the result of the war?
For several weeks, the pro-Russian separatists had the upper hand in an increasingly bloody conflict but the election of a new President, Petro Poroshenko, appeared to revive the armed forces and volunteer battalions.
An initial ceasefire failed in late June, and separatists were forced to pull out of key areas of northern Donetsk. By early August, Ukrainian forces were besieging the major cities of Donetsk and Luhansk.
But, amid reports that Russian irregulars and even servicemen were fighting inside Ukraine, the separatists recaptured Luhansk airport, regained ground and opened up a new front, driving towards Mariupol on the coast of the Sea of Azov.
The Minsk ceasefire was signed on 5 September and, despite repeated violations and hundreds more deaths, it is still nominally in force.
Ukraine's war: The human cost
- 4,035 killed and 9,336 wounded in eastern Ukraine
- Fatalities include 298 people on board flight MH17 shot down on 17 July
- 300 killed in 10-day period at end of October despite ceasefire
- 5.2 million people estimated to be living in conflict areas
- 454,456 internally displaced people within Ukraine
- 489,258 fled to neighbouring countries of whom 400,996 have gone to Russia
Source: Casualty figures from UN 29 October, UN figures for IDPs 7 NovemberCan the ceasefire survive?
All the signs point to a relentless push towards conflict. One rebel field commander had already described the current truce as a strategic pause. And after the rebel vote in Donetsk and Luhansk, President Poroshenko said a key plank of the ceasefire deal - partial autonomy granted to the rebel-held areas - should be abandoned.
Ukrainian forces, he said, should prepare defences against separatist attack in the cities of Mariupol and Berdyansk on the Sea of Azov as well as the north-eastern city of Kharkiv and the region of Dnipropetrovsk to the west of Donetsk.
Clashes intensified and spread in the conflict regions of Luhansk and Donetsk, and a large-scale build-up of military hardware was reported on the rebel side, with European monitors reporting sightings of heavy artillery and rocket launchers near the centre of Donetsk city.
Nato said the unmarked convoys involved "Russian tanks, Russian artillery, Russian air defence systems and Russian combat troops", but the government in Moscow said there was no evidence of that.What was wrong with the rebel elections?
Ukraine and the West insisted that under the Minsk ceasefire deal a local poll would be held as part of the special status subsequently given to Donetsk and Luhansk by Ukraine's parliament. Legislation provided for elections on 7 December, not a month earlier and organised by the separatists themselves.
Russian President Vladimir Putin said that all they agreed to in Minsk was to hold elections "in co-ordination with, not in line with" Ukrainian election plans.
However, the vote on 2 November had echoes of disputed 11 May referendums, which prompted the rebels in Donetsk and Luhansk to declare independence.Is there anything the international community can do?
Under the Minsk deal, a European observer team has been monitoring the ceasefire. However, they can do little more than observe the troop movements and escalating violence.
EU foreign policy chief Federica Mogherini has said it will be "extremely difficult if not impossible to start again" and the focus now is on supporting Ukraine.
Perhaps the main question at the heart of this is whether or not Russia wants eastern Ukraine to be stable.
Since March, the EU and US have tried to halt Russian involvement by imposing sanctions on key Russian individuals and companies linked to state finance, energy and arms. But there now appears to be little mood among Europe's leaders for any extension of economic measures.
What does Russia want?
President Vladimir Putin's aims are unclear. He backed the Minsk peace deal and, after months of talks, Russia agreed a deal to resume gas supplies to Ukraine.
What is not known is whether Mr Putin is prepared for a resumption of full-scale hostilities.
While the Kremlin has repeatedly denied supplying troops and sophisticated military hardware to the rebels, Alexander Zakharchenko, the Donetsk rebel leader, said in August that 3-4,000 Russian citizens had been fighting alongside the rebels. The recent surge in violence has brought fresh reports of troop and artillery movement.
One question that remains unanswered is whether Russia feels it needs a land corridor to Crimea.
Although a costly bridge or tunnel is due to be built from the mainland across the Kerch Strait to the peninsula, if the separatists were to capture Mariupol, that would pave the way for access further west along the coast to Crimea.
Are Russia's concerns legitimate?
Ukraine's geopolitical tug of war between the West and Russia all began in November 2013 when then-President Yanukovych pulled out of a deal on closer ties to the European Union at the last minute.
That decision and a subsequent deal with President Putin for cheaper Russian gas supplies sparked protests that ultimately brought Mr Yanukovych down.
So Russia, fearful of Nato reaching its borders, has concentrated on maintaining the regions with which it has closest ties in its orbit.
Ukraine is not in Nato but the alliance says member states can supply arms individually. Ukraine said in September that those deliveries had begun.
There were also unconfirmed reports that US military advisers had helped Ukraine in its major offensive against the rebels in July-August.