The United States, Canada and Mexico have "relatively few" differences on agricultural trade, the three countries' agriculture ministers said after meeting on Tuesday to discuss the renegotiation of the North American Free Trade Agreement.

There are some "irritants" for each country, however, in the run-up to NAFTA renegotiations, U.S. Secretary of Agriculture Sonny Perdue told a joint news conference at the Port of Savannah, Georgia.

"Now is not the time to talk about them. These are family discussions that need to take place," Perdue said. He compared the 23-year-old trade relationship to a marriage.

Renegotiation of NAFTA was a key campaign promise of U.S. President Donald Trump, who has pledged to shrink goods trade deficits that stood at $63 billion with Mexico and $11 billion with Canada last year, according to U.S. Census Bureau data.

While the United States has criticized NAFTA's impact on domestic manufacturing, it has recognized the agreement's benefits to agriculture.

"We've come together to acknowledge that by and large, NAFTA has been a favorable agreement for our three (agriculture) sectors in all three countries from an agricultural perspective," Perdue said. "That is the communication I gave to President Trump."

In a joint statement, the ministers said: "While even the best trading partnerships face challenges from time to time, our agricultural differences are relatively few in the context of the $85 billion in agricultural trade that flows between our three nations each year."

Perdue is meeting with Canada's minister of agriculture, Lawrence MacAulay, and Mexico's secretary of agriculture, Jose Calzada, in his home state for several days. It was the first trilateral meeting among the ministers since Trump took office in January.

U.S. trade negotiators are expected to address Canadian market access for U.S. dairy, wheat and wine. Faster trade dispute settlement procedures and a more streamlined approvals process for biotech products are also likely to be among issues negotiated.

Farm groups are urging the Trump administration not to undo gains made by the original trade deal or risk triggering retaliatory tariffs on farm goods. NAFTA is credited with quadrupling U.S. agricultural exports since its implementation in 1994.

"Agriculture is not the reason these negotiations are being done. It's a lot more to do with manufacturing," said David Salmonsen, senior director for congressional relations for the American Farm Bureau Federation.

"We don't want to see anything rebound on agriculture that would cause any new barriers to be constructed."