Matthew Heath is receiving medical treatment, multiple sources told AFP, with a family spokesperson confirming Tuesday night that "he is still very much in the fight of his life."

Heath, who was arrested in September 2020 for alleged "terrorism," has been accused by President Nicolas Maduro of spying and plotting attacks on oil and electrical installations.

"We are monitoring Matthew's health and welfare as closely as possible, and we are in regular contact with Matthew's family," a State Department official who spoke on condition of anonymity said in an email.

Heath's lawyer, Guillermo Heredia, said the ex-marine was "already out of danger."

Heath is not the only American detained amid tensions between Washington and Caracas, which has accused the White House of plans to overthrow the Maduro regime.

Airan Berry and Luke Denman, two US veterans accused of a failed sea raid seeking to overthrow Maduro in May 2020, were sentenced the same year to 20 years in prison on terrorism charges.

In addition, five former Citgo executives -- four Venezuela-born American citizens and one with US permanent residency -- have been held in Venezuela since 2017, accused of corruption.

Washington demands the release of all.

Two Americans -- Cuban-American Jorge Alberto Fernandez and former Citgo executive Gustavo Cardena -- were returned to the United States in March after being released from prison in Venezuela following a high-level US delegation's meeting with Maduro.