Russian concern over NATO enlargement fair; US doesn't want Ukraine in group: Trump envoy

US President Donald Trump's envoy to Ukraine, Keith Kellogg, said Russia's concern over the eastward enlargement of NATO was fair and the United States did not want to see Ukraine in the US-led military alliance.

Asked by US network ABC News about a Reuters report that Russia wanted a written pledge over NATO not enlarging eastwards to include Ukraine and other former Soviet republics, Kellogg said: "It's a fair concern."

"We've said that to us, Ukraine coming into NATO is not on the table, and we're not the only country that says that - you know I could probably give you four other countries in NATO and it takes 32 of the 32 to allow you to come in to NATO," he told ABC late on Thursday. "That's one of the issues that Russia will bring up."

"They're not just talking Ukraine, they're talking the country of Georgia, they're talking Moldova," Kellogg said, adding that a decision on U.S. views of NATO enlargement was for Trump to make.

Kellogg said the sequencing of the peace talks would include an attempt to merge the two memorandums drafted by Ukraine and Russia into one single document with talks in Turkey on Monday.

"When we get into Istanbul next week we'll sit down and talk," Kellogg said, adding that the national security advisers from Germany, France and Britain would join discussions on the memorandum with the United States.

Kellogg said Trump was "frustrated" with Russia because he had seen "a level of unreasonableness" from Russian President Vladimir Putin. He scolded Russia for striking Ukrainian cities and said he had told Ukraine to turn up to talks.

A conservative estimate of dead and injured in the Ukraine war - from both sides combined - totals 1.2 million, Kellogg said.

"That is a stunning number - this is war on an industrial scale," Kellogg told ABC.