Robinhood Markets and Interactive Brokers Group Inc. took steps Thursday to curtail trading in several high-flying stocks, including GameStop Corp. and AMC Entertainment Holdings Inc.

Robinhood restricted transactions on those stocks and others, according to a blog post. Interactive Brokers said it wouldn’t allow clients to take new options positions in names incuding AMC, GameStop and BlackBerry Ltd.

“In addition, long stock positions will require 100 per cent margin and short stock positions will require 300 per cent margin until further notice,” Interactive Brokers said in a statement.

Robinhood also restricted trading in shares of Nokia Oyj, which climbed 20 per cent over the past three days.

“We’re committed to helping our customers navigate this uncertainty,” Robinhood said in the blog post.

Reddit users helped fuel a blistering rally in GameStop, the video game retailer, burning short sellers and hedge funds. The stock, which ended the year at US$18.84 a share, posted whopping gains, climbing as high US$513.12 in early trading Thursday. The stock rose 2.7 per cent to US$357.02 at 9:45 a.m. in New York.

The episode pitted enthusiastic amateurs against professional traders, resulting in billions of dollars of losses for hedge funds that were forced to close out their positions.

On Wednesday, Charles Schwab Corp.’s TD Ameritrade also curtailed transactions on GameStop, AMC and other securities. Amid the heightened volatility, trading platforms including TD Ameritrade, Robinhood, Schwab and Fidelity all experienced technical problems.