China’s politically charged trade surplus with the United States widened to a record $31.05 billion in August, compared with $28.09 billion in July, customs data showed on Saturday.

The amount surpassed the previous record of $28.93 billion set in June.

The August surplus with the U.S. was larger than China’s overall surplus of $27.91 billion for the month.

China’s large trade surplus with the United States has long been a sore point in relations and is at the center of an increasing bitter dispute between the world’s two biggest economies.

Beijing and Washington have slapped each other with tit-for-tat tariffs in recent months and threatened more duties on each other’s goods. Talks aimed at easing tensions have yielded no major breakthroughs and both sides look to be digging in for a long fight that could weigh on global growth.