"The most powerful nation on earth, our neighbor, did worse than us." López Obrador said -- after noting that comparing the two countries was in "bad taste."
López Obrador has both defended and praised former President Trump in recent weeks. He called Mark Zuckerberg "arrogant" last month after the Facebook CEO blocked him from the platform.
"I felt he was very self-important and very arrogant," López Obrador said, according to Reuters. "A court of censorship like the Inquisition to manage public opinion ... This is really serious."
López Obrador also told President Biden that he had a good working relationship with the previous Trump administration.
"I must mention that we do have a very good relationship with the now president of your country, Mr. Donald Trump," he told Biden in a call before he was sworn in, The New York Times reported. "Regardless of any other considerations, he respects our sovereignty."
As of early Tuesday, at least 181,809 people have died in Mexico from the coronavirus since the start of the pandemic, according to data from Johns Hopkins University. The U.S. death toll recently surpassed 500,000, but its population is 2.6 times larger.
Biden called the milestone "truly grim" and "heartbreaking" Monday night, noting how the pandemic has taken more American lives than WWI, WWII, and the Vietnam War combined.
"That’s more lives lost to this virus than any other nation on Earth," Biden said.
Mexico has administered about 1.7 million vaccine doses, while the U.S. has given 64 million shots. The country is trying to beef up its supply of Pfizer vaccines with Russian and Chinese shots, and late Monday it received its first shipment of 200,000 doses of the Russian Sputnik V vaccines.
López Obrador, who has been criticized for his handling the coronavirus pandemic in Mexico, tested positive for the virus last month. He blamed rich countries for "hoarding" vaccines and demanded the U.S. vaccinate the millions of Mexicans living in the states -- with or without legal documents.
Mexico has had over 2 million confirmed COVID-19 cases, but the low level of testing means the real number is probably several times that amount.
The Associated Press contributed to this report