He added that he had "asked Secretary of State (Mike Pompeo) to closely study" the situation.
The South African government insists that its land redistribution measures are not about invading and seizing land but about expanding opportunities for black South Africans to take over agricultural land that is now lying fallow.
The government said the land reform should be implemented in a way that increases agricultural production, improves food security and ensures that the land is returned to those from whom it was taken under colonialism and apartheid.
"Reforming the land distribution and ownership will be good for South Africa", said political analyst Nic Borain.
Critics of the land policy say instead of seizing farmland from whites, such households should be given title deeds, turning millions into property owners.
Mr Trump's tweet comes days after it was announced that his wife, Melania, will travel to Africa in October for her first major solo global trip as first lady. There's black genocide in the USA.
However, the South Africa president said it would be done in an ordered manner and there would be no land grabbing.
Since 1994, the government has offered compensation to willing sellers of farmland in order to promote fair distribution, but the slow pace of land reforms led to a proposal of direct action a year ago.
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League spokesman Brian McCarthy declined comment Friday and reiterated his statement Thursday night, saying "constructive" discussions are ongoing with the union.
Though South Africa's constitution has not yet been amended and the government has not seized any major agricultural land, the prospect has sent panic through some white farming communities, who worry the policy will strip them of their land, cause land prices to plummet, or make them the target of potentially violent land seizures.
The State Department did not immediately respond to a request for comment about whether it has begun studying the issue.
South Africa has hit out at efforts to "divide" the nation after US President Donald Trump waded into the country's debate about land reform.
A range of measures was then considered, including a proposal for the government to take land in exchange for "just and equitable" compensation, less than the market would likely demand.
Updates with South Africa response in second paragraph.
President Donald Trump's tweet on land issues in her country was "based on false information".
But plans to change the constitution have yet to be approved by parliament, and there is a vigorous debate in South Africa about how land redistribution would work - and whether seizures could be economically damaging as they were in post-independence Zimbabwe.