‘This Week’ Transcript: Ambassador Samantha Power

April 13, 2014— -- Below is the rush transcript for "This Week" on April 13, 2014. It may contain errors.

(BEGIN VIDEOTAPE)

ANNOUNCER: Starting right now on ABC's This Week, Ukrainian special forces clash with pro-Russian militants. Both sides report casualties. Is this the start of war? We're live on the ground with all the breaking details.

The Contender:

UNIDENTIFIED MALE: Are we supposed to consider you the frontrunner now?

ANNOUNCER: On the road with Kentucky Senator Rand Paul. How the rising star is shaking up the GOP.

And, Boston Strong.

UNIDENTIFIED MALE: This is our (EXPLETIVE DELETED) city. Stay strong.

ANNOUNCER: One year later, a city facing new security fears ready to rise again.

From ABC News, This Week with George Stephanopoulos begins now.

(END VIDEOTAPE)

GEORGE STEPHANOPOULOS, HOST: Good morning, let's get right to that breaking news. A dangerous escalation in the crisis in Ukraine with gun battles between government troops and masked Russian protesters.

There are reports of new casualties. And the U.S. is warning Russia to stand down now.

UN Ambassador Samantha Power is here live for an exclusive interview after this report from ABC's Alex Marquardt on the scene in Ukraine. Good morning, Alex.

ALEX MARQUARDT, ABC NEWS CORRESPONDENT: Good morning, George. As you just said this is an extremely significant and dangerous escalation here in eastern Ukraine this morning. Ukraine says units from their equivalent of the FBI have now been deployed to the town of Slovyansk as part of what they're calling an anti-terrorist operation aimed against armed pro-Russia forces that yesterday seized government buildings, including the police headquarters.

Ukraine's interior minister says there have been dead and wounded on both sides. At least one Ukrainian officer has been shot and killed.

So far, the Ukrainian forces have not been able to take back the buildings.

We're about 10 miles outside of Slovyansk on our way there just passing through many of the new checkpoints that have sprung up around the town. They're manned by pro-Russian activists waving pro-Russian flags, stopping cars, looking inside. At many of them, they're blocking access to the town.

Across eastern Ukraine for the past week, we've seen government buildings violently seized by anti-government protesters, many of whom want to be closer to or even a part of Russia. The U.S. has directly accused Russia of being behind this new wave of unrest, which Moscow has denied.

Washington says many of the armed men that we've seen seizing these buildings over the past 24 hours have the very same uniforms and guns that Russian forces had when they annexed Crimea last month.

Moscow has warned Ukraine now to crack down on these protests, saying that violence against Russian-speakers here would provoke a response. And with around 40,000 Russian troops, as well as artillery and fighter jets lining that border with eastern Ukraine, the big fear now is that this new violence will give Russia an excuse to invade -- George.

STEPHANOPOULOS: OK. Let's get more now from our chief global affairs correspondent Martha Raddatz. Martha, this raised a lot of alarm bells with U.S. officials. Secretary Kerry immediately on the phone with his counterpart.