NANJING -- Investment contracts worth 3.4 billion US dollars were signed by enterprises from both China and the United States during a forum held Saturday in eastern China's Jiangsu province.

The investments, mostly directed toward the United States, were made among 85 enterprises from 21 Chinese cities and 20 US cities that participated in the second US-China Cities Forum on Economic Cooperation and Investment.

A total of 42 investment projects were involved, covering 21 sectors -- including manufacturing, energy conservation and environmental protection, electronic information, chemical and pharmaceutical.

At the forum, four Chinese enterprises also announced their investment projects in the United States, which totaled 70 million US dollars.

More than 30 Chinese mayors and representatives of over a hundred Chinese enterprises, including private and small companies, attended the forum. The 100-strong delegation of US enterprises headed by 20 mayors came to the event, as the United States stepped up export-boosting efforts to rejuvenate its sluggish economy.

"We hope that the investment from China will boost the US economy," US Treasury's Assistant Secretary Marisa Lago said at the opening ceremony.

Lago said Chinese investment increased the fastest among all foreign investors in the United States, citing an annualized growth rate of 53 percent from 2005 to 2010 and 6 billion in total investment during the period.

The forum, jointly sponsored by Chinese and US finance ministries, this year sought to form contracts on the basis of agreements reached between China and US top officials over the past year, including Chinese President Hu Jintao's visit to the United States in January 2011.

It also focused more on investment this year compared with the first one held in Seattle from April 19-20 last year, during which no contracts were inked.

US delegates have been trying to make the most of the tour. They came to China days before the forum, acquainting themselves with local officials and enterprises, looking for every chance, even if a chance only to make themselves first heard.

Mike Rawlings, mayor of Dallas, Texas, said to revitalize the economy and increase jobs, the United States needs the support of international cooperation and foreign capital.

Rawlings hoped that his trip to China would help deepen cooperation between his city with Chinese cities, and particularly, to open a direct air route from Dallas to China.

In contrast to the eagerness on both sides, Chinese investment in the United States only accounts for a small share in the country's total foreign investment.

Aside from a limited understanding of US local markets, another major obstacle for Chinese enterprises to invest in the nation is barriers set by its top officials, said Mei Yuxin, a researcher at the Chinese Academy of International Trade and Economic Cooperation under the Ministry of Commerce.

To address the concerns, Lago explained US foreign investment review principles in her speech.

China's Finance Minister Xie Xuren said at the opening ceremony that China and the United States have different resource advantages, and strongly complement each other in economic development.

Both countries were working to speed up economic restructuring and promote major reforms, which have presented bigger room for cooperation, he said.

The two economies should expand cooperation in more sectors, especially in energy and environmental protection, biomedicine and infrastructure, so as to turn opportunities into tangible results, Xie said.

China and the United States are each's second largest trading partner. Bilateral trade currently totals 446.6 billion US dollars.