Zambia's government voiced concern on Friday about the "unnecessary financial strain" that would be caused by a new rule requiring its citizens to pay bonds of up to $15,000 to obtain some types of U.S. visas.

Starting August 20, U.S. President Donald Trump's administration will require applicants from countries with high rates of visa overstays - including Zambia and neighbouring Malawi - to post a bond of $5,000, $10,000 or $15,000 under a pilot programme for some tourist and business visas.

"While the (U.S.) government has a prerogative to initiate policy changes, the Zambian government views this development with serious concern, given its potential economic implications on trade, investment, tourism and people-to-people exchanges," Zambian Foreign Minister Mulambo Haimbe said in a statement.

"This includes the unnecessary financial strain on Zambian nationals."

The move comes as Trump cracks down on illegal immigration, boosting resources to secure the border with Mexico and arresting people in the U.S. illegally.

The bond amount will be returned if the applicant leaves the U.S. within the allowed window of time and complies with all the terms of their visa status.

Even so, average household income in Zambia is roughly $150 per month, according to government data, making the bond a huge sum in the Southern African country.

"For most Zambians... this bond is not just unaffordable, it's laughable," said Anthony Mukwita, a Zambian international relations analyst and former diplomat in a Facebook post.

"It could drill a borehole and bring clean water to an entire village," Mukwita said. "Instead, it is being used to buy a chance at an American dream, a dream that's increasingly looking like a gated community with a very expensive entry fee."

In Malawi, Foreign Minister Nancy Tembo met a delegation from the U.S. embassy on Thursday to discuss the policy.

"The minister expressed concern on the policy's impact on law-abiding Malawian travellers and overall bilateral diplomatic relations," the Foreign Ministry said in a statement.