The US Internet giant said in a statement it "believes the plaintiffs' claims are without merit and will vigorously pursue all appeals."

The California company's statement offered few details on the case.

It said the 49th Civil Court of the Federal District of Mexico City has "entered a non-final judgement of US$2.7 billion against Yahoo! Inc. and Yahoo de Mexico" in the case.

The lawsuit was brought by Worldwide Directories SA de CV and Ideas Interactivas, and "alleged claims of breach of contract, breach of promise, and lost profits arising from contracts related to a yellow pages listings service," Yahoo! said.

Yahoo! shares were down 1.4 percent in after-hours trade on the news.

Yahoo! in October reported that its quarterly profit rocketed above US$3 billion, fuelled by the sale of part of its stake in Chinese e-commerce giant Alibaba.