(CNN) — A plan by Ecuador to allow the US military to use an airstrip on the Galapagos island of San Cristobal has drawn an outcry from politicians and activists in the South American country.

Critics say the move could threaten the fragile environment of the Pacific archipelago, a UNESCO World Heritage Site, and compromise Ecuador's sovereignty.

In a press conference earlier in June, Ecuadorean Defense Minister Oswaldo Jarrin said the Galapagos Islands, lying around 1,000 kilometers (625 miles) off the mainland, functioned the country's "natural aircraft carrier." The US military would use San Cristobal primarily for refueling aircraft involved in anti-narcotics operations, and would pay for upgrades to the island's small airport, he said.

Following fierce criticism, Jarrin stressed Monday that the Galapagos would not become home to a US military base nor any kind of permanent post. Foreign military bases are outlawed in Ecuador, according to a 2008 revision of the country's constitution by former left-wing prime minister Rafael Correa.

Protesters fear the US military could cause damage to the ecosystem of the Galapagos Islands. Dolores Ochoa/AP

Correa denounced the plan on Twitter , saying: "Galapagos is NOT an 'aircraft carrier' for gringo use. It is an Ecuadorian province, World Heritage Site, patriotic ground."

The Galapagos Islands, famed for their rich biodiversity which inspired Charles Darwin's theory of evolution, were named a World Heritage Site by UNESCO in 1978.

The 19 volcanic islands and their waters are considered to be of "outstanding universal value," according to UNESCO. The archipelago is home to many endemic species including giant tortoises, penguins, finches, hawks, and iguanas. Among its wealth of marine life are several species of shark including hammerheads and whale sharks, giant manta and eagle rays and sea lions.

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San Cristobal, which hosts the airstrip under contention, is the fifth largest Galapagos island. According to US non-profit Galapagos Conservancy, it is home to about 5,400 people, the second most populated island after Santa Cruz. Tourists frequently visit the island for its significant population of sea lions.

Last week, lawmakers voted in favor of a resolution by Galapagos assemblywoman Brenda Flor, compelling Jarrin, environment minister Marcelo Mata and Galapagos government council president Norman Wray to appear before parliament.

Jarrin must answer questions about the extent of the planned collaboration with the US military, while Mata and Wray will be asked about the potential environmental impact.

The airstrip is located on San Cristobal island. Chris J Ratcliffe/Getty Images for Lumix

On Facebook, Flor wrote : "I remain alert for my province and I am concerned about the impact that the development of these activities has, as well as the effects that can be generated on the ecosystem of our World Heritage Site."

In a statement posted on Twitter, Wray insisted that "there is not, nor will there be a foreign military base" on the Galapagos Islands.

There are already significant concerns about the environment of the archipelago. The number of tourists visiting the islands rose from 161,000 in 2007 to over 225,000 in 2016, the International Galapagos Tour Operators Association said, prompting calls for stricter regulation of the industry.