The front lines in eastern Ukraine changed significantly today. We saw it happen.

We headed out early to a church service near the Malaysia Airlines Flight MH17 disaster site, taking the same route we had for days, passing sunflower fields still dotted with wreckage.

Suddenly, rounding a corner, we saw two cars of rebel fighters. They jumped out, dived in the ditches and dropped to their bellies near a train track.

They waved us on urgently down the road. Something was brewing. 

At the next intersection, there were more rebels. We were told Ukrainian tanks were up ahead. They said, "Go if you like, but you might get caught between the Ukrainian army and us." Not a good idea.

Ukraine Russia separatists

A Ukrainian armoured convoy rolls into an area near the downed Malaysia Airlines Flight MH17, as the army clashes with pro-Russian separatists. A CBC News crew captured images of the convoy about five kilometres from Rozsypne, Ukraine. (Susan Ormiston/CBC)

We turned around, but before we could leave, one of the fighters rushed up, pleading with us, "Take my dog — at least he won’t die."

And then he shoved a black dog into our van.

"Drop it at the next safest town," he told us, closing the door and running back into position.

We carried on, passing through villages taut with nervousness. There was shelling in the city of Torez, where a train carrying the bodies of flight MH17 was loaded a week ago.

We gave the rebel dog some water and let it out in one of the towns.

At the crest of a hill in another, we stopped to survey the scene. We were about five kilometres from where the cockpit of flight MH17 had plunged into a sunflower field.

Suddenly behind us we heard the sounds of a convoy. Ukrainian armoured vehicles, waving the blue and yellow flag — about 20 of them artillery, anti-aircraft and armoured personnel carriers, rolling by us.

Yesterday this area was controlled by pro-Russian separatists. They headed down the hill into the valley, advancing against the rebels.

The heightened tension cancelled a planned visit to the crash site by an international observer team, along with Dutch and Australian aviation and forensic experts.