NATO said on Friday it was concerned by the ‘increasing sophistication’ and number of weapons deployed by pro-Russian rebels in eastern Ukraine, following the crash of a Malaysian Airlines jet there. ‘We are concerned about the growing number of heavy weapons being operated ... as well as the increasing sophistication of these systems,’ a NATO official said. ‘We have seen that Russia continues to allow mercenaries and heavy weapons to flow across its borders into Ukraine,’ the official added. Asked about what the US-led military alliance knew of the circumstances of the crash of flight MH17 with the loss of nearly 300 lives, the official said he could not comment on intelligence matters.