WASHINGTON (Reuters) - U.S. land borders with Canada and Mexico will remain closed to non-essential travel until at least March 21, the one-year anniversary of the restrictions to address COVID-19 transmission concerns, the U.S. government said Friday. The new 30-day extension is the first announced under President Joe Biden and comes as the White House has been holding meetings about potentially tightening requirements for crossing at U.S. land borders in North America, officials said. Canada has shown little interest in lifting the restrictions and recently imposed new COVID-19 testing requirements for some Canadians returning by land crossings. On Jan. 26, the U.S. government began requiring nearly all international air travelers to get negative COVID-19 test results within three days of travel, but has no similar requirements for land border crossings. In an executive order issued last month, Biden directed U.S. officials to “immediately commence diplomatic outreach to the governments of Canada and Mexico regarding public health protocols for land ports of entry.” It added U.S. agencies should submit a plan to Biden within 14 days “to implement appropriate public health measures at land ports of entry.” “The plan should implement CDC (U.S. Centers for Disease Control and Prevention) guidelines, consistent with applicable law, and take into account the operational considerations relevant to the different populations who enter the United States by land,” it said. Biden also directed a similar review of sea travel and to “implement appropriate public health measures at sea ports.”