TOKYO — Twitter Inc. and Japan's biggest homegrown social networking site mixi Inc. joined forces Wednesday to strengthen their ground against a rapidly expanding Facebook.

For Twitter, the partnership with a local social network could point to a new strategy as the San Francisco-based microblogging service seeks to accelerate global growth. Japan is the company's second-biggest market after the U.S. and has served as a key international testing ground of sorts.

Japanese was Twitter's first foreign language platform, and it opened its first overseas office in Tokyo earlier this year. In April, the company hired James Kondo in Japan as its first international country manager.

Kondo said he didn't know if Twitter would forge similar partnerships in other countries. But the company is keen to see what happens with the experiment, which launched with a limited Christmas-themed application, he said.

"This is going to be an interesting case," he told The Associated Press. "We're going to see what works and what doesn't work, and we're going to build on top of that as opposed to throwing out something that may not work."

For mixi, the announcement couldn't have come at a better time.

The seven-year-old Tokyo-based company had been the dominant social networking platform in Japan. Despite its massive popularity elsewhere in the world, Facebook failed to make much of an impact in the country. That is, until this year.

Data released this week from Nielsen NetRatings Japan showed that mixi stood in third place behind Twitter and Facebook in terms of unique visitors in October.

More than 14.5 million users visited Twitter, and 11.3 million went to Facebook, according to the Nielsen report. In contrast, about 8.4 million visited mixi. Google's social networking service was a very distant fourth.

Facebook has surged over the last year in Japan, in part due to the popularity of the hit movie "The Social Network." The Nielsen data indicates that it surpassed mixi midway through the year. Growing social gaming services GREE and DeNA also pose threats to mixi.

Twitter and mixi said they offer contrasting -- and mutually beneficial -- services. While Twitter is a public platform with real-time information, mixi is a closed network. Most users limit their networks to a small group of their closest friends.

Mixi hopes that by partnering with Twitter, it can better integrate public information and conversation into its tight-knit communities.

"Mixi rightly had a choice to do it themselves or partner with someone who's good at this," Kondo said. "And we're glad that they thought that Twitter would be a good partner. I think we can provide value that's distinctive."

Kenji Kasahara, mixi's founder and president, said that the two companies started talking after the March earthquake and tsunami. Both services were used extensively as critical information lifelines in the wake of the disaster.

Twitter in particular gained credibility in Japan after the earthquake. New users flocked to the site for real-time information about the nuclear crisis, electricity blackouts and aftershocks.

"Had our services been connected during the disaster, we would have been able to provide much better service for our users," he said at a joint press conference at mixi headquarters.

But for starters, mixi has created a "mixi Xmas 2011" page, through which its users can share holiday messages on both platforms and send "social gifts" to friends.

Other new joint products are also in the works. The companies said they hope to co-operate on emergency communications during disasters, location-based applications, advertising and business services.