Newly published documents from Edward Snowden have shed more light on American surveillance operations in the UK. The Intercept details how the NSA and GCHQ used information gathered by Menwith Hill Station, a massive but tightly sealed facility that intercepts satellite data transmissions worldwide. Among other things, the files appear to include evidence that links UK-based surveillance to American anti-terrorism campaigns outside official combat zones.

While many surveillance efforts focus on the internet’s connective "backbone" cables, Menwith Hill intercepts wireless signals, using an array of antennae and US government satellites to capture up to 335 million pieces of metadata in a 12-hour period. Previous reports — including an earlier Snowden leak — have already revealed some of its capabilities. But The Intercept includes more details, particularly about the UK’s involvement in "capture-kill" operations against suspected terrorists. It describes how the GHOSTHUNTER program traced the location of targets "when they log onto the internet," often in internet cafes. A different program called GHOSTWOLF, which let the NSA and GCHQ monitor traffic from Yemeni internet cafes, is part of a plan to "capture or eliminate key nodes in terrorist networks" by tracking their locations.

This leak fuels existing suspicions that the UK’s role in American covert drone strikes is greater than it admits — potentially implicating it in the civilian deaths that have resulted. In 2012, a Pakistani man took the GCHQ to court over the wrongful death of his father in one such strike, accusing the agency of passing "locational intelligence" to the CIA. The case was dropped in 2014, after the court decided that considering the case would involve accusing the US of war crimes.

In response to this latest report, the GCHQ told The Intercept that all its work "is carried out in accordance with a strict legal and policy framework," and "is entirely compatible with the European Convention on Human Rights." But the remaining secrecy around Menwith Hill, even to British lawmakers, is unlikely to reassure privacy and human rights advocates.