Factbox-What does Ukraine's constitution say about territorial changes?

By Yuliia Dysa

KYIV (Reuters) -Territorial questions are certain to be a key area of focus when Ukrainian President Volodymyr Zelenskiy and European leaders meet U.S. President Donald Trump for talks on Monday to map out a possible peace deal to end Russia's war in Ukraine.

Russia occupies around a fifth of Ukraine and the U.S. president has said "land-swapping" and changes to territory will be crucial for any settlement. 

Two sources briefed on Russian thinking said on Saturday that Putin and Trump have discussed a proposal requiring Ukraine to fully withdraw troops from the Ukrainian-controlled parts of the eastern Donetsk region.

UKRAINE'S CONSTITUTION ON THE ISSUE OF TERRITORY 

Any changes to Ukraine's territory would have to be settled in Ukraine by a referendum, according to the country's constitution.   

"Issues of altering the territory of Ukraine are resolved exclusively by an All-Ukrainian referendum," Article 73 says.

The question can be put to a referendum by popular initiative if the signatures of three million eligible Ukrainian voters are gathered from at least two thirds of the country's regions, it says. 

UKRAINIAN GOVERNMENT STANCE 

Ukraine, like its European allies, strongly opposes the idea of legally recognising any Ukrainian territory as Russian. But it has tacitly acknowledged it will almost certainly have to accept some de facto territorial losses. 

Zelenskiy has said talks to end the war should take the current front line as their starting point and cannot begin by Kyiv having to withdraw its troops from parts of its own sovereign territory that Russia does not control.   

He has said he does not have a mandate to give away any of the country's territory, and that tracts of state land cannot be traded around as if they were his private property.  

Zelenskiy has also said that if Kyiv withdrew troops from the heavily fortified eastern Donetsk region, it would open up Ukraine to the threat of Russian advances deeper into less well-defended Ukrainian territory. 

TRUMP'S STANCE 

The U.S. president has publicly criticized Zelenskiy for saying he could not violate the constitution by agreeing to give away territory. 

"I was a little bothered by the fact that Zelenskiy was saying: 'Well, I have to get constitutional approval'. I mean, he has got approval to go into war, kill everybody but he needs approval to do a land swap. Because there will be some land swapping going on", he told the press on August 11. 

UKRAINIANS' VIEW 

A clear majority of Ukrainians want a negotiated settlement, according to opinion polls, but they also oppose recognising Ukrainian land as Russian. 

The Kyiv International Institute of Sociology says that an opinion poll it conducted in June showed that 68% of those questioned oppose the idea of officially recognising "some parts" of occupied land as Russian, while 24% are open to this. 

The same survey showed that 78% are against the idea of giving up on land that Kyiv's troops still control. 

The pollster did not survey opinions in areas occupied by Russia.

(Reporting by Yuliia DysaWriting by Tom BalmforthEditing by Frances Kerry)