Travel restrictions at the U.S.-Mexico border have been extended for another month as both countries struggle to control the spread of the coronavirus.

The United States and Mexico have agreed to keep land borders closed to nonessential travel until Sept. 21 — that will be six months since the border first closed in March to slow the spread of the coronavirus.

"Mexican and U.S. citizens should avoid crossing borders unless the reason is considered essential," said Edgar Ramirez, a Department of Homeland Security attaché at the U.S. Embassy in Mexico, said in an announcement about the extension. "Don't forget, a global pandemic is the not the time to go shopping, make a visit or see family."

U.S. Ambassador Christopher Landau also weighed in on the extension on Twitter, writing that the continued border restrictions are unfortunate but important during the ongoing pandemic, and urging U.S. citizens not to travel.

"The vast majority of those crossing the border are U.S. citizens," he wrote, later adding in response to a comment that he was "really very frustrated" by U.S. citizens who continue to cross the border without an essential reason.

"It's a reciprocal agreement," he wrote. "Only essential travel is allowed across our land borders in both directions."