KINGSTON, Jamaica (AP) — Jamaica's energy and mining minister resigned from his powerful Cabinet post Tuesday, hours after disclosing that the U.S. State Department had revoked his visitor visa, possibly due to a police investigation of him.

Energy and Mining Minister James Robertson said he was not informed why U.S. visas for him and his wife, Charlene, were withdrawn, but he speculated the decision could be tied to allegations he was involved in a murder-for-hire plot.

U.S. officials declined all comment on the visa matter, citing privacy rules.

In his statement, Robertson said the murder-for-hire accusations by St. Thomas businessman Ian Johnson "have been, and remain, wholly rejected." Robertson was never charged and has filed a defamation lawsuit against Johnson, a district constituent who made the allegations in an unsuccessful application for political asylum in the U.S.

In his resignation letter to Prime Minister Bruce Golding, Robertson said he was stepping down immediately following conversations with Golding, Cabinet colleagues, and his wife and daughters.

"Recent events which include several unsubstantiated allegations have taken a heavy toll on my family and me. I am confident however that this matter will be resolved once given the opportunity and due process," wrote Robertson, who is also deputy leader of the governing Jamaica Labor Party.

Jamaican police have said they opened an investigation into criminal allegations against the energy minister, without specifying if the probe involved Johnson's allegation.

On Tuesday, Assistant Police Commissioner Les Green said he expected to provide an update on the investigation in the next day or two. He gave no other details.

Jamaica's Cabinet met Tuesday to address the situation. Phone calls made to the government's information minister, Daryl Vaz, went unanswered.

The Jamaica Observer newspaper, which first broke the news that a top minister's visa was revoked, said Robertson did not offer to give up his parliamentary seat or step down as Labor's deputy leader.

The prime minister has said he first alerted police about the "disturbing allegations" against Robertson in late October after Johnson visited him at a constituency office and handed him a handwritten letter outlining his assertions.

Golding has said he passed the letter to police commanders Nov. 1 and asked them to speedily investigate.

Later, in a sworn statement made while he was in Florida, Johnson alleged in his unsuccessful application for U.S. political asylum that Robertson was behind the death of Johnson's mother and had taken out a contract on his life, among other accusations.

Peter Bunting, a spokesman for the main opposition People's National Party, said the visa reversal by the U.S. was a cause of "serious concern" and would hobble Robertson's ability to do business as a government official.

"It is very exceptional and unusual for the U.S. government to take this action against a high government official of another country and we would have to assume that it was not done ... arbitrarily," Bunting said.

Robertson said he has asked his U.S.-based attorney to find out why his visa was canceled.

(Photo: www.men.gov.jm/gallery.htm)