(Adds quote from Doud, detail on potential trade talks with UK)
DES MOINES, June 7 (Reuters) - More than 14 percent of $140 billion in annual U.S. farm exports have been or will likely be hit by retaliatory tariffs in trade disputes with major buyers such as China and Mexico, a top U.S. trade negotiator said on Thursday.
Mexico imposed tariffs on American products including pork and bourbon on Tuesday, striking back against import duties on steel and aluminum imposed by U.S. President Donald Trump.
Republican-led farm states where rural voters helped propel Trump into office in 2016, such as Iowa and Kansas, stand to suffer from the retaliatory tariffs.
Mexico's response raised trade tensions and further complicated efforts to renegotiate the trillion-dollar North American Free Trade Agreement between Canada, the United States and Mexico.
Mexico is the largest export market for U.S. pork, which is likely being targeted for retaliatory tariffs more than any other commodity, said Gregg Doud, chief agricultural negotiator for the United States Trade Representative.
China has also imposed tariffs on U.S. pork and other products. It was the second-largest destination for U.S. pork by volume last year.
"Let's be frank, the lead tip of the spear in all of this right now is your pork," Doud told hog farmers at an agricultural event in Iowa.
Trump has threatened tariffs on up to $150 billion of Chinese exports as part of a separate dispute over Chinese intellectual property protections.
Separately, he withdrew last year from the Trans-Pacific Partnership promoted by Japan, the top destination for U.S. beef. The move is expected to help Europe become more competitive for meat sales.
"I am very concerned about the situation with Japan," Doud said.
To increase trade, the United States hopes to hold trade talks with the UK after Brexit, he said. An April agreement that allowed U.S. pork exporters to ship meat to Argentina for the first time in 26 years a win, he said.
"These things now that we have to fix are very, very difficult," Doud said. "This is going to get a little more difficult here in the short term."
Ty Rosburg, who transports hogs in Iowa and heard Doud speak, said he worried that trade disputes could hurt the farmers who are his customers by lowering pork prices. Still, he said he believed U.S. officials were attempting to improve trade.
"I guess at some point you have to trust they're working for the greater good and hope that we don't get bit too bad," he said. (Reporting by Tom Polansek Editing by David Gregorio and Leslie Adler)