China, Russia and Mongolia signed a development plan on Thursday to build an economic corridor that will boost transport links and economic cooperation among the three neighbors, the official Xinhua News Agency reported.

The plan comes after Chinese President Xi Jinping said Chinese companies invested nearly $15 billion in countries participating in Beijing's new Silk Road initiative last year, up one-fifth from 2014.

The plan was signed by Xi, Russian President Vladimir Putin and Mongolian President Tsakhiagiin Elbegdorj in the Uzbekistan capital of Tashkent.

Xi called on the three countries to build the economic corridor, strengthen cooperation in transportation infrastructure connectivity, port construction, industrial capacity, investment, trade and economy, cultural exchanges and environmental protection in an effort to expedite results, Xinhua said late Thursday.

"We three sides should actively engage in the discussion of building cross-border economic cooperation zones, enhance industrial tie-in, boost sub-regional cooperation in our adjacent areas, and promote the common development of our adjacent areas," Xinhua reported Xi saying.