OTTAWA (AFP) - The United States has agreed to keep its borders with Mexico and Canada closed until July 21, officials said Tuesday (June 16), extending travel restrictions for a third time because of the coronavirus pandemic.

Prime Minister Justin Trudeau announced the latest extension on the US-Canadian border, while Mexico's foreign ministry said its northern border also would remain closed.

The three countries, which have a three-way free trade agreement, closed their borders to non-essential travel for the first time on March 21 as the Covid-19 pandemic was taking hold in North America.

Cross-border trade has not been subjected to the closures.

"I can now confirm that Canada and the United States have once again, agreed to extend by 30 days until July 21 the current measures in place along our border," Trudeau told a daily briefing. "This is an important decision that will keep people in both of our countries safe," he said.

Mexico's foreign ministry said the travel restrictions on its 3,145km border with the United States will remain in force until July 21.

"Both countries will continue to seek to coordinate health measures in the border region," the ministry said on Twitter.

The US-Canadian border is the world's longest at 8,900km.

Prior to the pandemic, C$2.4 billion (US$1.7 billion) worth of goods and more than 400,000 people crossed the border each day on average.

Its closure has led to a massive drop in cross-border traffic - of up to 95 per cent, according to Statistics Canada - but trade has continued unabated.