Japanese Prime Minister Shigeru Ishiba has warned that negotiations with the White House would be difficult after President Donald Trump hailed "big progress" in the first round of talks between the two sides over trade and security ties.

Why it Matters

Negotiations such as those with Japan are a key test of Trump's hard-line tariff policy, which he has said will either bring about much better deals for the U.S. with its partners across the world or draw more investment into domestic production.

Japan is among the first countries to start open negotiations with the U.S. The president and other administration officials said the phones have been "ringing off the hook" with dozens of countries calling, eager to strike deals.

What to Know

"Of course, the negotiations will not be easy going forward, but President Trump has stated that he wants to give top priority to the talks with Japan," Ishiba said after Wednesday's talks with the U.S., which Trump attended, Reuters reported.

Ishiba said he had "received reports that frank and constructive discussions were held over a considerable period of time," Japan's Yomiuri Shimbun reported, adding: "I believe that the discussions will lead to further progress."