Russian Prime Minister Vladimir Putin is visiting China in a bid to boost diplomatic ties and overcome hurdles to increased trade and sales of his country's vast energy resources. Putin arrived Tuesday afternoon and met with Premier Wen Jiabao for talks following a formal welcoming ceremony. A series of agreements were to be signed following the meeting. Despite warming ties, the two countries have struggled to increase trade and agree on sales of Russian gas to fuel China's booming economy. Moscow is also unhappy with China's illegal copying of Russian fighter jets and other military hardware and recently announced the arrest of a Chinese man accused of seeking to buy military secrets. Russia and China have worked to overcome mutual distrust from the Cold War and have increased bilateral trade volume to $35.9 billion in the first half of the year, up 39.6 percent from the same period last year, according to official Chinese figures. But despite rounds of tough negotiations, they have failed to finalize a massive natural gas deal, mainly because of pricing disagreements. Russia is eager to link gas prices to oil prices as it does in Europe, but China says that is too expensive. Russian and Chinese officials say deals worth $7 billion are to be signed during the visit in fields ranging from mining to biotechnology and space exploration. The sides are looking for even more cross-border investment, and on the eve of Putin's visit, Chinese Vice Premier Wang Qishan called for more financial cooperation and accelerated construction of cross-border highways, railways, bridges, power grids, telecommunications links, and oil and gas pipelines. While bilateral relations are not always smooth, China and Russia appear closer on international issues. Last week, both vetoed a U.N. Security Council resolution condemning Syria for its brutal crackdown on pro-reform protesters that has killed nearly 3,000 people since March.