Recent reports coming out of disputed waters in the South China Sea are painting a picture of persistent tensions in the region, with new evidence emerging that Beijing is saving its harshest words for Philippine aircraft.

Headlines this week highlighted warnings frequently given by the Chinese navy to US planes flying near disputed islands, but it seems that they are getting the polite treatment.

According to a report from the BBC, China’s warnings to Philippine aircraft are much more menacing than those delivered to their American counterparts.

“Philippine military aircraft. I’m warning you again: Leave immediately or you will bear responsibility for all the consequences,” a voice can be heard saying. The tone was noticeably more aggressive than the warning given to the American airmen.

According to US airmen speaking in the BBC report, the warnings they receive are routine and have no effect on their operations.

In response to the reports, Philippine President Rodrigo Duterte issued a rare criticism of China’s actions in the region, urging Beijing to “temper” the warnings.

“You cannot create an island and you say that the air above the artificial island is your own. That is wrong. The right to innocent passage is guaranteed,” Duterte said on Tuesday, as quoted by Philippine news website Rappler.

“I hope that China would temper its behavior. I do not want to quarrel with China but at this time. America in case of saying ‘get out, get out,’ China will say ‘go in’. […] One of these days the hothead commander there will press a trigger,” he added.