Yahoo Japan operator Z Holdings Corp. and Line Corp. said Monday they have reached a basic merger agreement that will forge an internet conglomerate boasting over 100 million users in Japan with the aim of challenging U.S. and Chinese online behemoths.

"In the internet market, overseas companies, especially those based in the United States and China, are overwhelmingly dominant," the two firms said in a statement.

"Even when comparing the size of operations, there is currently a big difference between such overseas companies and those in Japan and other Asian countries, other than China."