Hackers reportedly infiltrated into the Twitter accounts of The New York Post and United Press International (UPI), posting fake tweets related to economic and military news.
While The New York Post announced it had been hacked, Washington-based UPI's Twitter account also posted a fake tweet saying Pope Francis had declared "World War III has begun."
In a statement, UPI confirmed that both its Twitter account and news website had been hacked.
Hackers posted tweets about "active combat" between the US and Chinese navy vessels in the South China sea on The New York Post Twitter handle.
The New York Post and UPI were investigating the hack.
Last week, the Twitter account of the US military command was suspended following an attack by hackers claiming to support the terrorist group Islamic State (IS).