The plan to start construction of the Thirty Meter Telescope on the Big Island has been thwarted for more than three weeks by a group of Native Hawaiian activists who say the construction will further desecrate a mountain that already has more than a dozen observatories.

Thirty Meter Telescope Executive Director Ed Stone said in a statement Monday that the group still wants to break ground on Mauna Kea, but they need to have a backup plan.

"We continue to follow the process to allow for TMT to be constructed at the 'plan B' site in (Spain) should it not be possible to build in Hawaii," Stone said. "Mauna Kea remains the preferred site."

The development bolsters the Native Hawaiian activists, who say they will not budge until the project moves elsewhere.

Protest leaders, who say they are not against science or astronomy , told The Associated Press that the Spain permit is a positive development, but it's not enough for them to end their blockade of Mauna Kea's access road, where more than 2,000 people have gathered at times.

"There's lots of good science to be done from the Canary Islands," said Kealoha Pisciotta, who has helped organize the protest on Mauna Kea. It would "be a win for everyone."

But she said there is no trust between the activists, who call themselves protectors of the mountain, and telescope officials.

Kaho'okahi Kanuha, another protest leader who has been arrested several times trying to block construction, said he hopes officials make the "right decision" and move the project to the Canary Islands.

"We remain committed to protecting Mauna Kea from further desecration, no matter how long it takes," he said.

Canary Islands Astrophysics Institute Director Rafael Rebolo told the AP on Monday that he received a letter from the head of the Thirty Meter Telescope saying its board recently decided "to proceed with the request to seek a building permit" for the island of La Palma.

"We are observing what is happening in Hawaii with the maximum respect," said Rebolo, the point man for the alternative site in Spain's Canary Islands.

"Our position is that we are here if the TMT project needs us," he said in a telephone interview.

After years of protests and contentious legal battles, the Hawaii Supreme Court last year ruled the telescope permits were legal, clearing the way for the construction to proceed.

Separately, the state Department of Land and Natural Resources granted a two-year extension to the deadline for starting construction last week. The new deadline is Sept. 26, 2021.

In October 2016, Thirty Meter Telescope officials first announced the backup location in the Canary Islands — Roque de los Muchachos Observatory on La Palma.

Rebolo said local officials who would have jurisdiction over a La Palma building permit for the new telescope solidly back the project and that the observatory site has already passed environmental impact evaluations.

"Our mountains are not sacred," he added.

Scientists selected Mauna Kea's summit for the giant telescope because the weather and air conditions there are among the best in the world for viewing the skies. The telescope would give researchers a view back to the deepest reaches of our universe and allow them to examine the time immediately following the Big Bang.

Once built, scientists are expected to use the telescope to explore fundamental questions about the universe , including whether there's life outside our solar system and how stars and galaxies formed. The large size of the telescope's mirror means it would collect more light, allowing it to see faint, far-away objects such as stars and galaxies.

Big Island Mayor Harry Kim, whom Hawaii's governor tasked with finding common ground among Native Hawaiian leaders, protesters and telescope stakeholders, said it would be a loss for his island and the state if the telescope was built in Spain.

"I thought this could be a good thing for Hawaii if done the right way," Kim said.

But the mayor also acknowledged that injustices against the Native Hawaiian community need to be addressed. "Part of the right way is a recognition of wrongs of past," he said.

The mayor said his responsibility is to find a better way forward that addresses the many complicated issues involved with the battle over the telescope, including the economics for the Big Island.

"If this opportunity is lost, and I do mean it, there will be a sadness on my part," Kim said. "Not only because of science and education and opportunity, part of my responsibility is to try to find ways to make a better economic base for this island."

He said he doesn't want his county's entire economy to be based on tourism like it is on the other islands in Hawaii.

On "Maui, Kauai, and Oahu, the vast, vast majority of those people on those islands and counties can no longer own a home because of what has happened economically," he said.

The telescope "was one of the ways — besides agriculture, beside where we develop resorts and how we develop resorts — of my long-range viewpoint of what would be better for this island."

A spokeswoman with Gov. David Ige's office was not immediately able to respond to a request for comment.

Last week, Spain's science minister, Pedro Duque, reiterated the government's full support for the Canary Islands as a Plan B site for the telescope and said the country is well-prepared to host it.

"We have all the necessary plans at all levels — the people, the speed, the systems, absolutely everything is ready if they want to come," Duque said.

The Canary Islands archipelago, located west of Morocco in the eastern Atlantic Ocean, is already home to several powerful telescopes. The Roque de los Muchachos Observatory hosts more than 20.