Argue that the junta regime is the best option in a field of terrible options.
Basically, this junta you're talking about, per the fact they are selling oil, is going to have some friends – maybe that's generous – trading partners. So, conjure up some bogeyman, something far worse than what the junta is, something which must be stopped at all costs. And then, sell this narrative along with the oil.
It is easy for the junta to covertly support radical no-chance rebellions to launch attacks on the oil supply (also, since this is the most important source of revenue, any rebellion group would be launching attacks on this supply), which will infuriate foreign buyers.
The foreign buyers want their oil supply to be reliable, cheap, and dependable. This threatens those interests. So, the radical terrorists which are attacking that supply (who may or may not be funded by the regime) are threatening the global order. These terrorists are trying to sow discontent and destroy the state from the inside. They are the evil ones.
Nothing the government is doing is cruel... it is what must be done. The government simply needs to paint itself as the well-intentioned extremist. Then issue propaganda like this:
It is the for the good of the country, to fight back against radicals who want to destroy the country's values and prestige on the international stage. The opposition are composed of traitors supported by these radicals. They are collaborators trying to undermine the great strides in development we have achieved over the last few decades!
This government is dedicated to the return of peace and prosperity. We do not want to fight this war, to keep up this quarrel, but what choice do we have when we have been savagely attacked1 by terrorists who have slaughtered hundreds of innocent civilians?2 Our people demand vengeance. We must fight these foes, these terrorists which want nothing but the destruction of our way of life. What peace can be brokered with those who wish to see nothing but our nation's destruction?
Idealistic foreigners might cast doubt on our methods. But they are too naïve to understand what our nation has gone through. If they were in our shoes, they would be fighting the same fight. When the last bastion of civilisation is under attack by barbarism3 from all sides, this is not the time for idle pontificating, it is the time to do what we have to do.
1: Conflict may or may not have been started by the government.
2: Civilians may or may not have been placed into harms way by the government.
3: Barbarisms may or may not be present. To quote Orwell, "Everyone believes in the atrocities of the enemy and disbelieves in those of his own side, without ever bothering to examine the evidence".