Islamabad - The US, far from the public perception and official claims of supplying Pakistan with substantive military hardware, is actually impeding Pakistans efforts to upgrade its capabilities especially in non-offensive systems. According to inside sources, only recently, the PAF, which has an agreement with Ukraine for the purchase of air to air refuellers, asked Ukraine to send a trainee plane so that the PAF personnel could familiarise themselves with the systems that were expected later. The Ukraine agreed to send the required aircraft which happened to be in the US. However, before it could fly to Pakistan, the US authorities on learning of its destination, impounded the plane. Earlier, the US had tried unsuccessfully to block the deal itself.