Intrade, an online prediction market, said it had ceased trading on its website immediately due to circumstances that may include "financial irregularities" and require further investigation.
Intrade allows spectators to bet on subjects ranging from entertainment to elections.
It made the announcement on its website and said the company had closed and settled all open contracts as of the close of business on Sunday, March 10.
"With sincere regret we must inform you that due to circumstances recently discovered we must immediately cease trading activity on www.intrade.com," the company said in the statement.
Intrade, which is based in Dublin, said that these circumstances might include "financial irregularities" and that the company would conduct an investigation in the coming weeks.
Like other online prediction markets, Intrade allows users to buy or sell shares that represent the likelihood of an event occurring.
The company said in November that it would no longer accept US customers because of what it called legal and regulatory pressures, after the US commodities regulator sued the exchange's owner for allowing unauthorised trading by US customers.