Help me identify this film (possibly anime)

While watching Fist of the North Star yesterday I remembered a movie I only saw once as a child. It was an animated movie and I am pretty sure from what I remember that it had at least some anime influence in it.

The story from what I remember that the resources of the earth were completely depleted and so the ?? planned to capture a phoenix and use the energy of the beast to power their cities, there was also something about a project to mine into the molten core of the earth to use the heat of the lava, and kids that were especially trained for military service.

Its easily 15 years back when I saw the film and I dont remember much, any help is greatly appreciated.