• Russia has "considerable firepower" and it is reckless to talk about defeating the country, said Jeffrey Sachs, who formerly advised the Soviet Union on economic reforms.
• Ukraine President Volodymyr Zelenskyy said Thursday that Russia's strategic defeat is "already obvious," but that the Kremlin "simply lacks [the] courage to admit it."
• Sachs said Finland's bid to join NATO makes it difficult to reach a negotiated outcome, and that it brings NATO and Russia "right to the knife edge," though not everyone agrees.

Russia has "considerable firepower" and it's reckless to talk about defeating the country, according to a former economic advisor to the Soviet Union.

Jeffrey Sachs, now an economics professor at Columbia University, said the U.S. seems to believe it can beat Russia militarily, and the West is supporting Ukraine in its effort to push Russia out.

"With that view, Ukraine decided not to continue negotiations that were underway" even though talks were advancing at the end of March, he told CNBC's "Street Signs Asia" on Friday. Instead, Ukraine "changed the tune and said that now, their goal is to defeat Russia."

"What it means is an escalation of the war, an escalation of global dangers, an escalation of the economic fallout and a lost opportunity to find an off-ramp to this conflict as was taking shape already," Sachs said.

U.N. Secretary-General Antonio Guterres said this week that he does not foresee Ukraine peace negotiations happening in the immediate future.

Ukraine's Ministry of Defence and the White House did not immediately respond to CNBC's request for comment, which was sent after office hours.

Ukraine's President Volodymyr Zelenskyy said Thursday that Russia's strategic defeat is "already obvious," but that the Kremlin "simply lacks [the] courage to admit it." He had previously said Ukraine will defeat Russia's invasion.

In late April, U.S. Secretary of Defense Lloyd Austin said the U.S. wanted to see Russia "weakened."

But Russia has a strong military and more than a thousand active nuclear warheads, Sachs pointed out.

"All of this talk of defeating Russia, to my mind, is reckless," he said.

'Tremendous danger'

There's no off-ramp from the "clear U.S. war aims" at this point, and that is a dangerous situation, said Sachs.

"I've lived through decades of reckless U.S. foreign policy, U.S. bravado, and I'm afraid that we're at it again," he said. "This is not to condone Russia's invasion."

"I believe that the dangers are very high and that there's a lot of naivete right now and Ukraine has bought into it."

There could be a lot of destruction, loss of life and "tremendous danger for the whole world," including in the form of economic spillovers, the professor said.

He added that Finland's expected bid to join NATO makes it difficult to reach a negotiated outcome, and that it brings NATO and Russia "right to the knife edge."

Not everyone agrees.

Michal Baranowski of the German Marshall Fund said NATO's potential expansion to the Nordic countries decreases the chance of conflict with Russia.

Instead, if countries such as Finland and Sweden are not part of the alliance, Russia is more likely to have a confrontation with them, he told CNBC's "Capital Connection" on Friday.

"Bringing Sweden and Finland [into NATO] makes our alliances more secure and military confrontation with Russia less likely, even though it's clear that Russia, of course, will not like this," said Baranowski, a senior fellow.