Last week’s Internet outage that pushed North Korean websites offline for almost two days was probably caused by a problem inside the country, not on an external connection, an Internet researcher said Monday.

“The impacted equipment was within North Korea,” said Doug Madory, a senior research engineer at Renesys. On Friday, he published a detailed look at the way the outage looked from the network level.

North Korea is connected to the Internet via two links and because the problems were observed on both connections, it stands to reason the problem was on the North Korean side, he said.

Data traffic instability on both connections suggests network routers in the DPRK were impacted, but despite this they mostly stayed up and on the Internet, he said.

So perhaps it was networking equipment deeper in the North Korean network which suffered the outage.”

But the data doesn’t answer the most interesting question: what went wrong?

“Was it the result of a cyber attack? Maybe. It could also have been a power failure, equipment failure or a misconfiguration by a network admin.”

North Korea’s state media on Friday said a cyber attack perpetrated by the U.S. and its allies was to blame. If an attack was to blame, it’s almost certainly too early to tell the parties behind it. Other possibilities for the outage include a network malfunction, configuration error or a power failure.

The allegations against the U.S. were relayed via Voice of Korea, North Korea’s international radio broadcaster.

To-date, there doesn’t appear to have been any mention of the outage in the domestic North Korean media. As no more than a few thousand people are thought to have Internet access, the outage probably wasn’t widely known anyway.