N.Korea carries out tests for missiles: think tank

North Korea has reportedly conducted motor tests to improve its long-range missiles after a failed launch in April. 

The US-Korea Institute at Johns Hopkins University said the North appears to have carried out at least two tests of large motors needed for rockets and worked on a launch platform. 

The institute examined commercial images of the Sohae satellite launch station between April and September and found that 34 fuel tanks had been moved and vegetation appeared to be burned, next to a flame trench stained with an orange residue.

Nick Hansen, an expert on imagery analysis, said North Korea may step up action after elections in both the United States and South Korea. 

North Korea defiantly went ahead with the rocket launch in April, saying it was trying to put a satellite in orbit, but it disintegrated just two to three minutes after blast-off.