Secretary of State John Kerry and Secretary of Homeland Security Jeh Johnson have sent a letter to Gov. Paul LePage outlining the rigorous steps they say the federal government would take to screen any Syrian refugees before accepting them into the United States.

The Maine Sunday Telegram obtained a copy of the letter on Saturday. Governors of all 50 states and of U.S. territories received a similar letter, The Associated Press reported.

The letters are an apparent attempt to ease fears expressed by LePage and other governors that some Syrians who are actually terrorists bent on attacking the U.S. may be posing as refugees. On Monday, LePage joined several Republican governors who said they would not allow Syrian refugees to be admitted into their states after the previous Friday’s terrorist attacks in Paris.

The five-page letter, dated Friday, opens with an explanation that it was written in response to “ongoing discussions by governors across the country regarding our refugee resettlement program.”

It describes a “multi-layered and intensive” process, “involving multiple law enforcement, national security, and intelligence agencies across the Federal Government.”

According to the letter, the world is facing an unprecedented outpouring of more than 4 million refugees from Syria, and many U.S. allies, including Canada, already have pledged to “share some of this responsibility and accept Syrian refugees into their borders.”

The U.S. already has agreed to accept at least 10,000 Syrian refugees this fiscal year, which the letter calls “a modest commitment.” It notes that Canada has agreed to accept 25,000 refugees.

States cannot dictate federal immigration policy, so it’s unlikely any governor would be able to stop the federal government from settling refugees. Lavinia Limon, president and chief executive of the U.S. Committee for Refugees and Immigration, said in a statement Monday that governors cannot legally block refugees from settling in their communities.

Nevertheless, 15 Republican governors and one Democrat – New Hampshire’s Maggie Hassan – made declarations Monday in response to the series of attacks carried out Nov. 13 by Islamic State terrorists in Paris that killed 130 people and wounded hundreds more.

The investigation into the attacks is continuing, including whether any of the terrorists came to Europe as refugees, possibly from Syria, which has been ravaged by conflict since 2011.

The letter says that only a small percentage of the Syrian refugees accepted into the U.S. would be “adult males who are not accompanied by children nor joining family in the U.S.,” adding that only “especially vulnerable” single men would be accepted, such as survivors of torture, LGBT individuals and those with disabilities. The overwhelming majority of refugees accepted would be “families, victims of torture, and children,” it says.

Refugee applicants would undergo a rigorous and comprehensive vetting and interview process, the letter says. Any “red flags” would immediately render the applicant ineligible for acceptance into the U.S., it says.

President Obama has said the U.S. would continue with its plan to accept up to 10,000 Syrian refugees. He also said Syrian refugees are the ones being harmed by terrorists and deserve compassion, not to be labeled dangerous.

Not all of Maine’s elected officials agree with LePage’s vow to use any lawful measure to keep Syrian refugees from settling in the state. Senate Democratic leader Justin Alfond of Portland has called LePage’s comments “morally repugnant” and described them as a cynical attempt to prop up his “anti-immigrant agenda.”

LePage spokeswoman Adrienne Bennett did not immediately return a call and email seeking comment Saturday night.