Vice President Xi Jinping reiterated that territorial disputes with neighboring countries should be resolved through negotiations when addressing the opening ceremony of the China-ASEAN Business and Investment Summit and Forum in Nanning, capital city of Guangxi Zhuang Autonomous Region on Friday.

"We are firm in safeguarding China's sovereignty, security and territorial integrity and are committed to resolving differences with neighbors concerning territorial land, territorial sea and maritime rights and interests peacefully through friendly negotiations," Xi was quoted as saying by the Xinhua News Agency.

Premier Wen Jiabao Thursday said in Brussels on the sideline of a China-EU summit that China would make no concession in affairs concerning the country's sovereignty and territorial integrity, People's Daily reported.

Both the Chinese leaders' remarks were made amid mounting tensions between China and Japan after the latter "nationalized" the Diaoyu Islands.

Analysts say tensions over the islands are very likely to persist after Japanese Prime Minister Yoshihiko Noda was reelected leader of his party.

Noda was easily reelected president of the ruling Democratic Party of Japan (DPJ) Friday, beating other candidates by a large margin, Xinhua reported.

"We will steer diplomatic policy calmly and with a comprehensive view, without provoking or responding to provocation," Noda was quoted by Reuters as saying to the ruling party members before the vote.

But the reelection may only secure his position as the prime minister for a few more months, as the inconsistency of the DPJ's many policies has made the party rather unpopular among Japanese voters, Wang Pin, a researcher on Japanese studies at the Chinese Academy of Social Sciences, told the Global Times Friday.

"If Noda, rather than the president of the more radical Liberal Democratic Party, is reelected as prime minister, less changes are expected to occur to the situation in the Diaoyu Islands," Qu Xing, director of the China Institute of International Studies, told the Global Times.

But both analysts agreed the Diaoyu Islands spat will persist for a long time, no matter which Japanese party eventually wins the election.

Chen Lianzeng, deputy director of China's State Oceanic Administration (SOA), said Thursday that safeguarding China's sovereignty and marine rights over the Diaoyu Islands would be a long-term and critical struggle, urging all SOA subsidiaries to be fully aware of the struggle's severity, according to Xinhua.

Meanwhile, Yuichiro Hata, Japan's Land, Infrastructure, Transport and Tourism Minister, said Japan will not allow China's fishery administration ships to exercise rights of jurisdiction within Japan's exclusive economic zone.

He added that Japan would be prepared for a protracted struggle against Chinese official ships, the Kyodo News reported.

The maritime tensions over the Diaoyu Islands seem to have also extended to trade between the two countries.

The Japan External Trade Organization's office in China complained that Chinese customs in Shanghai have begun inspecting all items of some products imported from Japan, instead of just a section of the items, adding that inspections have also increased in other cities such as Beijing and Tianjin, NHK World reported.

Although Japanese Finance Minister Jun Azumi clarified Thursday that Japan had found no evidence so far to prove China had tightened customs inspections, Japanese Minister of Economy, Trade and Industry Yukio Edano called on China Friday to abide by international rules after the reported customs problems, according to Japanese media.

The Global Times' inquiry via e-mail to the Shanghai Customs had not received any reply as of press time.

In the meantime, China's National Tourism Administration said Friday that it has canceled a plan to attend an international travel fair to be held in Japan.

China's foreign ministry spokesperson Hong Lei said Friday that economic and trade relations between China and Japan have obviously been affected by Japan's decision to "purchase" the Diaoyu Islands, Xinhua reported.

"This is a situation that we are reluctant to see," he was quoted as saying by Xinhua.

"The Japanese should face squarely the reality, correct the erroneous action and come back to the track of resolving the dispute through dialogue and negotiation."

He also said the wrong decision of the Japanese government has ruined many plans for the ceremony marking the 40th anniversary of the normalization of diplomatic ties between China and Japan scheduled to be held in Beijing next week, Xinhua reported.

Agencies contributed to this story