President Trump’s controversial tweet urging Secretary of State Mike Pompeo to “closely study” the “large-scale killing of farmers” in South Africa drew a note of caution Thursday from Republican Sen. Jeff Flake (Ariz.).

Flake, chairman of the Senate Foreign Relations subcommittee on Africa, challenged Trump’s grasp of the facts on farmer killings and urged him not to tweet about foreign policy using information from “one news report.” The senator is a frequent Trump critic who is retiring at the end of his current term.

Trump’s tweet, which aired a false narrative pushed by white nationalists, had referred to Fox News host Tucker Carlson’s denunciation of a plan by South Africa’s ruling party to pursue constitutional changes that would allow the government to redistribute land without compensation.

“I think it’s important for the president, if he’s going to conduct foreign policy by tweet, to be more careful and not to base something on one news report,” Flake said in brief remarks on the Senate floor. “These things matter."

Flake said he disagreed with expropriating land without compensation but called the government effort “simply a proposal” that has “not been implemented.” He said there is “no evidence to suggest that there is a large killing of farmers.”

“The evidence suggests that the number of farmers that have been killed over the past year is about one-third of the level that was reached in the 1990s,” Flake said. “So I would just encourage the president to be more careful when he tweets, to not conduct foreign policy by tweet."

With his tweet, Trump waded into a highly charged debate in South Africa over land redistribution and gave prominent voice to concerns on the far-right about the alleged plight of white South Africans.

The tweet drew a response overnight from the South African government, which wrote from its own account: “South Africa totally rejects this narrow perception which only seeks to divide our nation and reminds us of our colonial past.”

Flake sought to calm the waters, saying, “We have a good relationship with and want to remain close to” the South African government.

“We in the Congress believe that we are their friends, and we want to move forward in ways that will bring the best to South Africans and a good partnership with our country,” he said.