No I do not have any official statement to support it but there are many fact from which it can be infer that it has much longer range than the officially stated range.
1) Saraswat in one of interview stated that " agni v ka range 5000 KM hai lekin usko jarurat ke hisab se badhaya ja sakata hai. tum use 6000 chaho to 6000 karlo, 7000 chaho to 7000 karlo" he stops at 7000.(Video available in youtube)
2) With some what inferior technology, 16 ton Agni IV can travel at a distance of 4000 KM with 1.5 ton of pay load. It reaches a height of over 800 KM. So with a normal trajectory it may reach a distance of more than 4500 KM to 5000 KM as energy will be used in covering distance rather than gaining height. So How much advance Agni V with a weight 50 Ton may travel. Simply not as much as 16 ton Agni 4 but much much more than that.
3) In re entry phase, Agni V has a velocity of Mach 24 which means 8KM/Second. With a velocity of 6 KM/Second, you can reach an ICBM range which is 5500 KM. Chinese missiles with much lesser velocity reaches 8000 to 10,000 KM (As per Chinese claim) So Agni V can easily reach more that 10,000 KM.