Malaysian Prime Minister Najib Razak must walk a diplomatic tightrope on his visit to China next month. Najib's trip is intended to celebrate the 40th anniversary of bilateral ties, and he will have to strike a balance between showing enthusiasm for the historic occasion and conveying respect for the relatives of Chinese passengers aboard Malaysia Airlines flight MH370, which went missing last month. "We have to be sensitive towards the feeling of the families, and large-scale celebration seems not very possible," said Najib's political secretary, Wong Nai Chee. "Without the missing flight incident, we could have [had] the celebrations in a different manner. "We are not saying we should not celebrate, but we have to do it in an appropriate way to take care of the sentiment of the families." Relatives of the passengers have expressed anger and frustration over the Malaysian government's handling of the affair, accusing them of withholding key information that could have saved time. Tension turned into wails of grief when Najib announced on March 24 that the flight, with 227 passengers and 12 crew on board, "ended" in the southern Indian Ocean. Families protested outside the Malaysian embassy in Beijing, and accused the prime minister of being "inhumane" to their plight. Wong said they faced a dilemma on whether to make the announcement regarding the fate of the flight. Officials were aware the assessment would be questioned because no wreckage had been found and the conclusion was based in part on the analysis of British satellite telecommunications company Inmarsat. "It is reasonable for the families to demand direct evidence," he said. "But the accusations targeted at us should be based on objective facts rather than on speculation and conspiracy theories." Wong said the missing flight saga would not have a long-term impact on ties. Regarding regional tensions over sovereignty claims in the South China Sea, Wong said Beijing would lose political trust in Southeast Asia if it continued to unilaterally assert its claims. PLA warships ventured into waters near James Shoal for an oath-taking ceremony to defend China's sovereignty. The shoal is also claimed by Malaysia and Taiwan. "The move of China is controversial," Wong said. "It is not appropriate for a nation to unilaterally declare sovereignty when we are still seeking discussions over the disputes. "You cannot repeatedly take provocative moves, and at the same time, want other people to believe that you have no intention to invade." But the territorial dispute would not be high on Najib's agenda because "it is not necessary for the two nations to enlarge their differences at an inappropriate time", Wong said.