Apple Inc has asked suppliers to ensure that shipments from Taiwan to China comply with the latters customs regulations to avoid them from being held for scrutiny, according to a Nikkei report on Friday. Sino-US trade tensions have escalated following US House of Representatives Speaker Nancy Pelosi and a congressional delegations visit to Taiwan. The iPhone maker told suppliers that China had started enforcing a long-standing rule that Taiwanese-made parts and components must be labeled as made either in "Taiwan, China" or "Chinese Taipei", the report added, citing sources familiar with the matter. Apple did not immediately respond to a Reuters request for comment. Apple iPhone assembler Pegatron Corp said its mainland China plant is operating normally, in response to a media report that shipments to Pegatrons factory in China were being held for scrutiny by Chinese customs officials. Taiwanese supply and assembly partners Foxconn and Pegatron are ramping up manufacturing efforts as Apple is set to launch its new iPhone in September.