Right, but see the details for estimated range and the map. Not that India has any foreseeable need to nuke Argentina but it's not in range. It's entirely possible the public data is wrong and the Agni VI has a global range.
But by definition if you can put something into a 350x350 km low earth orbit (something like 7800m/s total delta V) you could also deliver a re-entering payload from your launch site to any other spot on earth, within the limitations of the inclination you're launching to.
Multiple sources think that the real range is an ICBM level. And the Indian government purposely limits it's range. No strategic reason to communicate a larger range than needed and why have an headline that reads, "India develops capability to nuke Europe or US"?
Ballistic intercepts are still very difficult and not always certain to work. Interception is only possible within a specific trajectory window with limited number of shots.
The missile defense we commonly hear about these days is used against lower speed , shorter range and altitude missiles:
But by definition if you can put something into a 350x350 km low earth orbit (something like 7800m/s total delta V) you could also deliver a re-entering payload from your launch site to any other spot on earth, within the limitations of the inclination you're launching to.