U.S. President Donald Trump and Chinese President Xi Jinping on Saturday agreed not to impose new tariffs, Washington and Beijing said, but trade strains will be rekindled if the two countries fail to make concessions on contentious matters within 90 days.

The United States agreed to put off levying additional tariffs and to leave the current rate on $200 billion of Chinese goods at 10%, not raising them as previously planned, after Jan. 1.

The world's two biggest economies, meanwhile, agreed to talk about technology and intellectual property rights issues within 90 days, but "if at the end of this period of time, the parties are unable to reach an agreement, the 10% tariffs will be raised to 25%," the White House said.

Although Washington and Beijing also confirmed that they will start negotiations to eliminate all tariffs, a failure to resolve an array of thorny issues before the clock runs out could spark another round in their trade war.

The agreements came at the first face-to-face meeting between Trump and Xi since November 2017, on the sidelines of the Group of 20 summit in Buenos Aires.

"We'll be discussing trade and I think at some point we're going to end up doing something that's great for China and great for the United States," Trump said at the outset of the summit, adding that he has "established a wonderful relationship" with Xi.

Xi said to Trump, "Only with cooperation between us can we serve the interests of both peace and prosperity," expressing hope that the U.S.-China trade dispute would be resolved through dialogue.

Trump is likely to have urged Beijing to carry out concrete reforms to stem its alleged unfair business practices, including intellectual property and technology theft, while Xi may have proposed to end the ongoing trade war by accepting some requests made by Washington.

With concern growing that escalating trade tensions have been dragging down the broader economy, China promised to open its markets further and buy more U.S. products in an attempt to curb its massive trade surplus with the United States.

China has agreed to "purchase a not yet agreed upon, but very substantial, amount of agricultural, energy, industrial, and other product from the United States," adding it will start buying "agricultural product from our farmers immediately," the White House said.

In addition, Trump and Xi confirmed that Washington and Beijing will "immediately begin negotiations on structural changes with respect to forced technology transfer, intellectual property protection, non-tariff barriers, cyber intrusions and cyber theft, services and agriculture."

The U.S. president has apparently been trying to not only rectify the trade imbalance with China but also to sell U.S. products in Chinese markets without anxiety about intellectual property and technology theft, diplomatic sources said.

Since earlier this year, the two countries have engaged in tit-for-tat rounds of punitive tariffs on each other's imports. Sino-U.S. ties have deteriorated sharply, sparking fears of a "New Cold War."

So far, the United States has imposed tariffs on $250 billion of Chinese imports -- or about half the goods it imports from China each year -- in response to Beijing's alleged theft of intellectual property and technology, as well as other trade complaints.

In retaliation, China has levied tariffs on more than 80 percent of all goods imported from the United States.

Trump had threatened to impose tariffs on all Chinese imports if he failed to "make a deal" with Xi.

Many economists have warned that intensifying trade strains between the United States and China would deal a crushing blow to the global economy, which has been on a recovery track.

At their summit, Trump and Xi also exchanged views on the denuclearization of North Korea.

"Great progress has been made with respect to North Korea," the White House said, adding, "President Trump, together with President Xi, will strive, along with (North Korean leader) Kim Jong Un, to see a nuclear free Korean Peninsula."

Trump was quoted by his office as saying, "This was an amazing and productive meeting with unlimited possibilities for both the United States and China. It is my great honor to be working with President Xi."