The Kremlin has never fully defined the goals of its invasion, which it said was partly intended to protect Russian-speakers in eastern Ukraine. But it no longer speaks of trying to force a change of government in Kyiv as Ukraine has steadily reversed early Russian territorial gains.

Moscow's troops were driven back from a lightning advance on the capital at the start of the invasion, launched on Feb. 24, and have successively been forced out of the adjacent Sumy and Kharkiv regions, and areas near Mykolaiv in the south.

Kyiv denies persecuting Ukraine's Russian-speakers and has vowed to retake all lands seized by Moscow since 2014, when Russia captured Ukraine's Crimean peninsula and backed armed separatists who took control of parts of Donetsk and Luhansk.

On Thursday, Kremlin spokesman Dmitry Peskov appeared to limit the Ukrainian territory that Russia now sought to incorporate to the four provinces that it has unilaterally declared as its own: Donetsk, Luhansk, Kherson and Zaporizhzhia.

None of these are fully under Russian control, and Peskov implied that in Zaporizhzhia's case, Russia had given up on capturing the remainder.

Asked whether Moscow planned to incorporate any more regions beyond those four, Peskov said:

"There is no question of that. At least, there have been no statements in this regard. But there is nevertheless a lot of work ahead to liberate the territories; in a number of new regions of the Russian Federation there are occupied territories that have to be liberated."

He then issued a further qualification:

"I mean part of the Donetsk Republic, as well as what became part of the Russian Federation [through annexation], and then was re-occupied by Ukrainian troops."

'NEW TERRITORIES'

Moscow proclaimed in October that it had annexed the four provinces - which it calls the "new territories" - shortly after holding so-called referendums that were rejected as bogus and illegal by Kyiv, the West and a majority of countries at the United Nations.

While Moscow made clear it wanted to take full control of Donetsk and Luhansk - two largely Russian-speaking regions collectively known as the Donbas - it left unclear how much of Zaporizhzhia and Kherson it was annexing.

If Russia were to seek to secure only the parts of Zaporizhzhia that it held at the time of the referendums - behind a section of the front line that has hardly moved in months - it would be renouncing any ambition to take the northern third of the province, as well as the industrial provincial capital of the same name, which straddles the Dnipro.

Last month, Russia's army was forced to quit all the parts of Kherson province that it had controlled on the west bank of the Dnipro River, including the provincial capital, the city of Kherson.

Ukrainian forces control around 40% of Donetsk province and have retaken a sliver of Luhansk.

(Reporting by Reuters; editing by Guy Faulconbridge)

By Kevin Liffey