Intertek Group, a provider of quality and safety services, has acquired US software testing firm National Software Testing Labs (NSTL) and Australian minerals and environmental specialist Northern Territory Environmental Laboratories (NTEL) for a combined £13 million.

Philadelphia-based NSTL, which specialises in testing mobile devices and PCs, was bought for $24 million (£12 million) from Lloyd Holder and Gerald Roche.

Meanwhile, the group purchased Darwin-based NTEL from its four management shareholders for A$2.4 million (£1 million).

The acquisitions are the 13th and 14th respectively for Intertek this year.