A senior advisor to Ukraine's President Volodymyr Zelenskyy says the country is not willing to give up any land to Russia.
Alexander Rodnyansky was speaking as NATO countries say they will send more equipment to Ukraine to boost their defences.
Its Secretary-General, Jens Stoltenberg, called the conflict the "biggest threat to our security in a generation" and announced a boost in defence spending and the deployment of "four new battle groups" in Bulgaria, Romania, Hungary and Slovakia.
There are already around 40,000 troops spread from the Baltic to the Black Sea.
On talks between Ukraine and Russia, Mr Rodnyansky told The Hard Shoulder issues - such as around recognition of the Russian language - are not the sticking points.
"Those things are easy, those are just PR stunts on the part of the Russians and they can use them if they want to sell it to their local population as if they've achieved something.
"When it comes to our territorial integrity, of course there won't be any negotiation.
"There won't be anything on the table - we're going to stand firm behind our territorial integrity.
"We're not going to give up any land".
Asked what President Zelenskyy expects from the peace talks, he says: "He has to give them a try, he has tried to meet face to face with the Russian leader for many months now - if not years.
"There was clearly no interest, and now we know why: because there was never meant to be a peaceful solution on the part of the Russians.
"They were always interested in the military solution.
"But we have to give peace a try, and obviously we are giving it a try".
'We need it now'
He says they have two demands of international leaders.
"The message is clear and simple: we have two major priorities on which we are hoping that we will get more support.
"One is obviously militarily; we're hoping that we'll get more ammunition and arms supply that we can use.
"There's plenty of Soviet ammunition still lying around in Germany that's not used - we can make use of it, we need it now.
"As well as other facilities and other military technologies that will help protect the sky.
"Number two, of course, we need further economic pressure on Russia.
"As we can see Russia's increasingly adapting to the economic environment, to the new sanctions.
"It's strengthening its currency again - that cannot be tolerated - we need to make sure that there is an oil embargo and a gas embargo in Europe for the import of Russian oil and gas".
'Catastrophe' of Mariupol
And he says Ukrainian forces are successfully keeping Russian troops back in many areas.
"We're hearing that there is more or less a stalemate in certain regions.
"We've pushed them back around Kyiv, so they're not having any success when it comes to storming our capital.
"In the north, they're facing serious opposition from our army - in fact our army has been able to push them back.
"In the south and in the east, there are more serious issues for us; they've been able to encircle the city of Mariupol.
"There is 95% of buildings there have either been destroyed or damaged - the civilian population is under immense stress and suffering.
"So there is really a catastrophe that's going on there".
The European Council - including Taoiseach Michael Martin - is meeting in Brussels to discuss ways of cutting reliance on Russian gas.
They will discuss the latest developments on the ground, the humanitarian situation and refugees.
And leaders will examine how the EU can act more quickly when facing crises, including around defence investment and funding.
US President Joe Biden also announced new sanctions "in alignment with the European Union" that would target more than 400 individuals and entities, including oligarchs and Russian defence companies "that fuel the Russian war machine".