Shelling and fighting between Ukrainian forces and pro-Russian separatists prevented a group of international investigators from reaching the Malaysia Airlines Flight 17 crash site.

As Reuters reports, a deal between Malaysian Prime Minister Najib Razak and the pro-Russian rebels had been struck earlier that would ensure that the investigators would be protected as they went about their work in the area currently under control of the separatists. Fighting has put a wrinkle in things.

International monitors said the fighting itself could affect the crash site, underlining the growing complexity of trying to establish who shot down the plane."

Some on the ground see foul play:

According to the Malaysian prime minister, the rebels have fulfilled two of their three obligations, returning both the bodies of the MH17 passengers as well as the black boxes. What remains, allowing access to the crash site for an investigation, is the last.

Update

While we're on the topic of the intense fighting between pro-Russian rebels and Ukrainian forces, it seems important to note that the United States has just issued more proof that not only is Russia delivering heavy artillery for pro-Russian rebels, but it is actually firing rockets in eastern Ukraine from its own territory.

From NPR:

In a four-page document titled Evidence of Russian Shelling into Ukraine, released Sunday, blast marks from rocket launches in Russia and craters in Ukraine can be seen, the State Department says.

The document also shows "self-propelled artillery only found in Russian military units, on the Russian side of the border, oriented in the direction of a Ukrainian military unit within Ukraine."

The images, taken over the past few days, track with what Kiev has been screaming about as Ukraine tries to wrest control of its eastern region back from the separatists and international investigators try to confirm what happened with Malaysia Airlines Flight 17.