At this point the talks between the US and Ukrainian delegations have concluded (as of Sunday night), and up next is the separate meeting with the Russians, which has begun Monday.

"We're moving closer and we're closer to peace than we ever have been," Walz told CBS' Face the Nation. "And now we have technical teams, actually, with Ukrainians and Russians at the same facility, conducting proximity talks."

That's when he revealed a major new focus of negotiations for the Monday talks. "We now going to talk about a Black Sea maritime ceasefire so that both sides can move grain fuel and start conducting trade again in the Black Sea," Walz described.

Reaching a lasting ceasefire deal would allow both warring countries to "move grain, fuel, and start conducting trade" in the sea again, he said.

Also high on the agenda will be discussions of the front line, the issue of territories, and the achievement and maintenance of sustainable peace. "We'll talk the line of control… details of verification mechanisms, peace keeping, you know, freezing the lines where they are," Walz noted.

The issue of "broader and permanent peace" and "security guarantees" are also on the table as the diplomatic engagements proceed.

As the talks in Riyadh have reportedly begun Monday, the Russian ruble has continued to strengthen on to the expectation of a peace deal, by 09:30 GMT gaining over 1% against the US dollar in the over-the-counter market.

Meanwhile, Ukraine's president Volodymyr Zelensky has condemned the continued aerial attacks on Ukraine. Overnight Ukraine's military says it shot down nearly 60 inbound Russian drones. Both sides say they've agreed to a US-brokered pause on attacks against energy infrastructure - both other attacks have persisted.

Zelensky called on allies put more pressure on Russia "to stop this terror". He said in a fresh televised statement that "since March 11, a proposal for an unconditional ceasefire has been on the table, and these attacks could have already stopped. But it is Russia that continues all this."

"Our team is working in a fully constructive manner, and the discussion is quite useful. The work of the delegations continues," Zelensky said in reference to the Sunday Riyadh meeting with the US delegation.

"But no matter what we're discussing with our partners right now, Putin must be pushed to issue a real order to stop the strikes, because the one who brought this war must be the one to take it back," he added.