Deborah, there has been constant pressure across that semicircular arc of the front in Ukraine itself. The Russians slowly making progress. There was an assumption that in many respects, Ukraine would struggle to hold the line. It's now entered Russia itself, flipping this whole situation on its head. But in reality, how long can it stand to stay on Russian soil?

Well, I imagine that there was probably quite a bit of surprise for the Ukrainians that they've been able to push so far so quickly. Of course, they would have had intelligence. They could see the lack of Russian defenses along that border region, but they would have anticipated a much stronger Russian response much, much faster, but that didn't happen. I was speaking to a source yesterday who gave a sense of the aims of this mission. One of them, this source said, was to create basically a buffer zone, a gray zone, not inside Ukrainian territory, but inside Russian territory, to help better protect the communities, the people who live in Sumi region, for example, and Kharkiv region and have been under heavy bombardment from Russian forces on the other side of the border. Another aim is to have greater leverage over Vladimir Putin, to hold some territory that could maybe be negotiated for Russian-held territory in Ukraine. There's clearly, and this is something that Vladimir Zelenskyy said yesterday, there's clearly a desire to increase what he calls the Exchange Fund of prisoners, detainees, Ukrainians, Ukrainian soldiers and others held in Russia being swapped for the many Russian soldiers that it seems Ukraine has managed to capture so far in this offensive.

Then another goal is really to show to the Russian people that the war is much closer than they think. They've had two and a half years of Russia's full-scale invasion, largely contained within Ukraine. Yes, the Ukrainians have increasingly been launching drone and missile strikes, including deep into Russia. But this is the first time that they have tried a concerted land offensive. And they're not just going in and coming out. They're going in, they're taking land, and they clearly plan to stay there if they can.

Deborah Haynes in Lviv for us this morning. Thank you so much.