The International Criminal Court has "immediately" started investigating whether war crimes have been committed in Ukraine, its chief prosecutor announced Wednesday.

ICC prosecutor Karim A. A. Khan had indicated earlier this week that he would move to request an investigation, though he first required authorization for a pretrial chamber or a referral from the court's member states.

On Wednesday, 38 members made the referral -- marking the largest referral in the history of the ICC, according to the British Foreign Office. Khan's office can now move straight into its probe.

"With an active investigation now underway, I repeat my call to all those engaged in hostilities in Ukraine to adhere strictly to the applicable rules of international humanitarian law," Khan said in a statement. "No individual in the Ukraine situation has a licence to commit crimes within the jurisdiction of the International Criminal Court."

Neither Russia nor Ukraine is among the court's 123 members, but Ukraine has provided authorization for an investigation in its territory, Khan said.

-ABC News' Conor Finnegan

U.S. Secretary of State Antony Blinken expressed little optimism for talks between Ukraine and Russia.

"The demands that Russia put on the table were beyond excessive, they were of course nonstarters and what we've seen repeatedly is that Russia goes through the pretense of diplomacy to distract and continue on its aggressive path," Blinken warned.

Blinken also addressed the Russian people in a press briefing Wednesday.

"This is President Putin's war. This isn't the Russian people's war. It's becoming clearer by the day that the Russian people oppose it. Members of the Russian military oppose it and had no idea what they were being sent to do. And now the Russian people will suffer the consequences of their leader's choices," Blinken said.

"The economic costs that we've been forced to impose on Russia are not aimed at you. They're aimed at compelling your government to stop its actions, to stop its aggression. And just as millions of us around the world stand together against Moscow's aggression, we also stand together with you as you demand that your leaders end this war," Blinken added.

Blinken said the U.S. is documenting Russian attacks that may have targeted civilians and wants to ensure there's accountability, among other things.

"This is shameful. The number of civilians killed and wounded, the humanitarian consequences will only grow in the days ahead," he said.

Blinken accused Russia of hitting schools, apartment budlings, hospitals, roads, critical infrastructure like drinking water, electricity, and gas - along with Kyiv's TV power and Babyn Yar.

He praised the U.N. General Assembly's vote to condemn the Russian invasion and commented on the five states who voted against the resolution saying, "as Groucho Marx once sort of said, this is not very much a club that I would want to be a member of."

He said the Biden administration's working very actively to get U.S. assistance into Ukraine including lethal defensive aid, but declined to comment on whether the U.S. or Europe would potentially providing war planes to Kyiv.

-ABC News' Conor Finnegan

The Pentagon announced it will postpone an intercontinental ballistic missile test previously scheduled for this weekend to demonstrate that the U.S. is a "responsible nuclear power."

Pentagon press secretary John Kirby called out Russia for elevating its nuclear alert status and said the U.S. did not take its decision lightly.

“Such provocative rhetoric and possible changes to nuclear posture involving the most consequential weapons and our respective arsenals is unacceptable,” said Kirby. “The United States has not taken any similar steps.”

“In an effort to demonstrate we have no intention in engaging in any actions that can be misunderstood, or misconstrued, the Secretary of Defense has directed that our Minuteman-III intercontinental ballistic missile test launch scheduled for this week to be postponed,” said Kirby.

Kirby said that “in this time of heightened tensions” the U.S. and the international community saw Russia’s announcement as “dangerous and irresponsible and, as I've said before, an unnecessary step.”

Kirby said the decision to cancel the test is not a step back in U.S. readiness, and does not imply it will cancel other routine activities to ensure "credible nuclear capability."

-ABC News' Luis Martinez

The 40-mile-long Russian convoy has "stalled" and is not moving at a rate indicating they have solved their problems, a senior U.S. defense official said.

The official said Wednesday they do not have perfect visibility into what's happening on the ground, but they believe the stall is due to several factors, one of which is stiff Ukrainian resistance north of Kyiv to include attempts to attack the convoy.

"We have some indications that they have also at places and at times tried to target this convoy," the official said of the Ukrainian forces.

Another factor continues to be "significant logistical and sustainment challenges."

"As for the food and fuel ... our assessment is that they are suffering shortages of both," the official said.

As in days past, the official emphasized that "We would expect that the Russians will ... learn from these missteps and the stumbles and will try to overcome them."

"We think there's some degree that the purpose of this convoy is to help with resupply as well. So ... I think they're going to try to alleviate the food and fuel shortages that they've experienced," the official said.

About 82% of the Russian forces that were arrayed at the border are now inside Ukraine -- up from approx 80% yesterday, according to the official.

Russia has now fired about more than 450 missiles against Ukraine since the beginning of the invasion, the official said.

The official said that it is not always clear when civilians are being deliberately targeted by Russian attacks or are just being hit by errant strikes meant for nearby military targets.

Airspace over Ukraine remains "very contested," the official said.

Russians continue to fare better in the south. "They have been achieving more progress down there," the official said.

- ABC News' Matt Seyler