Wall Street stock futures are sharply lower this morning after North Korea claimed to have successfully tested a hydrogen bomb for the first time (more below). The dollar is flat against the euro but lower against the yen. Gold, the ultimate ‘safe haven’ asset, has risen 0.7% to a two-month high. Aside from the political scare, markets are also spooked by Nikkei’s report of Apple cutting production of iPhones in response to mounting inventories.

Today’s must-read story is by Fortune’s Matthew Ingram on why Twitter (TWTR) wants to expand its character limit to 10,000 from its current ceiling of 140 characters, a move that has angered many of the social site’s loyal users.

Here’s what else you need to know.

1. Pyongyang learned to stop worrying. Markets, not so much.

World stock markets have taken the news of Pyongyang’s hydrogen bomb test badly. International experts have cast doubt on the claims but the news adds to a list of geopolitical concerns that have weighed on sentiment since bourses re-opened after the holidays. Elsewhere, the global Brent crude oil benchmark has fallen to its lowest level in 12 years, on the perception that the main consequence of the Saudi-Iran spat will be a lack of cooperation in restricting oversupply. But the chief concern appears to be in China again, the Apple news being seen as proof of slowing demand in the world’s second-largest economy. Fresh capital outflows have driven the ‘offshore’ yuan level sharply lower, although the mainland’s benchmark stock index, the CSI 300, has bounced 2%.

2. German migrant debate boils over after New Year crime wave

The debate over large-scale immigration into Germany has turned nasty again after an evidently coordinated wave of sexual assaults and street thefts against women on New Year’s Eve by gangs of what eyewitness and media reports describe as “Arab or north African-looking” young men. Around 90 women were sexually molested or robbed in Cologne. No-one has yet been charged. The incidents have triggered public outrage, while politicians and police have urged people not to jump to conclusions and link the attacks to the million asylum-seekers who arrived in Germany last year.

3. Federal Reserve releases minutes.

The Federal Open Markets Committee will release the official minutes from its most recent meeting on Dec. 15-16, where the group decided to raise interest rates for the first time in nearly a decade. Economists and investors will be looking for more clues as to how the Fed will approach future rate increases as well as why there were no dissents against the move even though certain governors had favored keeping interest rates near zero for longer.

4. Consumer Electronics Show kicks off.

The Consumer Electronics Show takes over Las Vegas today through Saturday. The supershow features all the latest and greatest technology that’s in the works from companies big and small. The pre-show started Tuesday and already companies have unveiled a range of new ventures and products from industries as diverse as health care to automobiles and video games. Keynote speakers during this year’s show include Netflix (NFLX) CEO Reed Hastings, General Motors (GM) CEO Mary Barra, and IBM (IBM) CEO Ginni Rometty.

5. U.S. service industry update.

The Institute for Supply Management releases data on U.S. services industry performance for December today at 10 a.m. ET. The industry is expected to have performed decently, expanding at a similar rate to the month prior. That’s good news given the recent manufacturing slowdown. Factory activity in the U.S. shrunk for the second straight month in December, according to on ISM data released Monday.