KYIV, Dec 15 (AFP) - Russia is digging in for a long war in Ukraine and still wants to conquer the entire country, a senior Ukrainian military official said on Thursday.

Brigadier General Oleksiy Gromov told a military briefing that although he did not expect Moscow to launch an attack from Belarus, Russian was training new troops on its neighbour's soil and had moved military aircraft there.

Deputy Defence Minister Hanna Malyar, at the same briefing, warned against allowing complacency to set in after recent Russian military setbacks.

"The Kremlin ... is seeking to turn the conflict into a prolonged armed confrontation," Gromov said.

Malyar added: "We and the world should not relax, because the ultimate goal of the Russian Federation is to conquer all of Ukraine, and then it can move on."

Gromov did not say what Russia's aim might be in prolonging the already nearly 10-month-old war.

Ukrainian officials have portrayed the Kremlin as desperate to reverse recent military setbacks - which included a retreat from the southern city of Kherson after months of occupation - and secure victories to justify the war to the Russian public.

General Valery Zaluzhny, commander in chief of the Ukrainian armed forces, told the Economist magazine that Russian forces were doing all they could to prevent Kyiv from striking back.

"This is why you are seeing battles along the 1,500 km frontline ... they are constraining our troops in order not to allow us to regroup," the magazine cited him as saying in an interview published on Thursday.

"The next problem that we have is, first of all, to hold this line and not lose any more ground. It's crucial ... Our troops are all tied up in battles now, they are bleeding."

Zaluzhny said Moscow was preparing for a new assault early next year, possibly aiming for Kyiv.

The Kremlin has never fully defined the goals of its Feb. 24 invasion, which it said was partly intended to protect Russian-speakers in eastern Ukraine.

It said last week that it was still set on securing at least the bulk of the parts of east and south Ukraine that it has declared its own, but appeared to give up on seizing other areas in the west and northeast that Ukraine has recaptured.

Ukraine's military staff said Moscow's current main focus was on the eastern cities of Bakhmut and Avdiivka, but that Russian forces were shelling Kherson daily and trying to get a stronger foothold in the southeastern region of Zaporizhzhia.

"They understand that if they do not stretch the front now, then this winter will be a disaster for them," said Andriy Yermak, head of the Ukrainian presidential office.

Russia, which has also been attacking Ukraine's energy infrastructure, has ruled out a Christmas ceasefire. Gromov also dismissed the possibility of a ceasefire over the festive New Year period.

"There will be a total ceasefire only when not a single occupier remains on our land," he said.