GEOFF BENNETT: Sudan's military today agreed to send a representative to potential negotiations 16 days after an eruption of violence that has killed more than 500 people.

The street-to-street fighting and a humanitarian crisis has forced millions to flee their homes.

Nick Schifrin reports on the conditions and the U.S. evacuation of hundreds of American citizens since Friday.

NICK SCHIFRIN: In Saudi Arabia's Red Sea port of Jeddah, the USS Brunswick helped deliver salvation for hundreds of American citizens.

Their journey took days through desperation and destruction.

Most evacuees are on their own.

DR. MOHAMED EISA, Sudanese American Physicians Association: We saw going through all these roads dead bodies on the sides.

NICK SCHIFRIN: Dr. Mohamed Eisa is an obstetrician-gynecologist resident in Pittsburgh whose daughter is American.

He returned to his native Sudan to help bury his father and ended up caught in the crossfire of two factions that turned Khartoum into a war zone.

He escaped the violence a week ago for a five-day journey to Port Sudan and Jeddah.

DR. MOHAMED EISA: The worst part of it was the checkpoints at gunpoint that we were manually searched a couple of times.

Some of them were extremely friendly, extremely nice.

And some of them, you could see that they could flip at any point and basically pull the trigger.

So -- and that's why -- and that was a scary part, Nick, that you could tell there isn't any sort of pattern to this.

There isn't sort of instructions about how to deal with the innocent people.

NICK SCHIFRIN: Those checkpoints are run by the paramilitary group Rapid Support Forces, or RSF, who are currently fighting the Sudanese military for control of the country.

They have accelerated an already dire humanitarian crisis.

Millions of Sudanese are short of water, food and electricity.

And the medical system is on the verge of collapse.

Last week, artillery hit this hospital lobby and wounded 13.

DR. MOHAMED EISA: More than two-thirds of the hospitals are completely out of service for various reasons, whether they were bombarded, whether they were attacked, or they run out of medical supplies, or they - - even they run out of medical personnel.

If you escape getting a bullet, or if you escape getting a missile in your house, you will die from a medical problem that might not be even related to the war that's happening in the streets of Khartoum right now.

NICK SCHIFRIN: This weekend, the International Committee of the Red Cross delivered eight tons of mostly medical supplies to Port Sudan.

But the violence is so intense, the supplies can't move forward to the front lines, spokeswoman Alyona Synenko told us today from Nairobi.

ALYONA SYNENKO, International Committee of the Red Cross: We also have the general state of lawlessness with looting that is becoming widespread.

And it is extremely difficult and volatile security environment for our teams to be working in.

NICK SCHIFRIN: One of the hospitals in need is Khartoum's Al Nada.

The general manager told "PBS NewsHour," so many other facilities had been destroyed, they're performing 10 times their normal number of C-sections.

DR. MOHAMED EISA: In this particular institution, just the first day, we received about five babies that were sick.

Some of them, unfortunately, didn't make it, extremely difficult for the families to see the -- just the newly born babies just dying in front of their eyes because of the lack of basic medical needs.

NICK SCHIFRIN: One of those providing for those needs was Dr. Bushra Sulieman.

That's him on the left with Dr. Eisa.

He's an American gastroenterologist who flew to Sudan from his Iowa home to train Sudanese students and treat patients.

DR. MOHAMED EISA: Bushra was a hero, simply.

Bushra was a hero.

I don't think there are any -- enough words to describe Bushra and what he was doing in Sudan.

NICK SCHIFRIN: Dr. Sulieman remained in Khartoum, despite the violence, despite the risk to himself, to treat some of the thousands of those wounded by war.

How did he die?

DR. MOHAMED EISA: I think that was the -- that's the most difficult part of it.

He was stabbed to death, unfortunately, from a group of unknown people, that we believe the reason behind that was just -- unfortunately just robbery.

Sudan has not just last Bushra, but Sudan has lost thousands of patients that he was taking care of, lost hundreds of students Bushra was teaching, medical professionals.

And, also, Sudan lost a big part of the humanitarian work Bushra was doing.

Sudan just simply lost a nation.

NICK SCHIFRIN: And for so many Sudanese, there is no warship coming to the rescue, no sanctuary, when even those who heal become the targets.

For the "PBS NewsHour," I'm Nick Schifrin.