King's daughters, Patty King and Karen Williams, made the accusations in separate, but identically worded, affidavits filed over the weekend
"I believe my father was poisoned and that he was administered foreign substances to induce his premature death," they said in their affidavits. "I believe my father was murdered."
Both women accuse LaVerne Toney, King's business manager, and Myron Johnson, his personal assistant, of neglect.
An attorney for Toney said the daughters were chasing a check.
"This is absolutely about money," Eric Brent Bryson told CNN, adding the charges were "absolutely ridiculous" and "unfounded."
King died May 14 in home hospice care in Las Vegas at 89.
No investigation was conducted at the time of his death. And King's attending physician listed the cause as multi-infarct dementia, which is caused by a series of small strokes.
But the daughters say that two of King's associates gave him medication to induce diabetic shock.
John Fudenberg, the coroner for Clark County, Nevada, told CNN that initial autopsy results found "no evidence to substantiate the allegations." But full forensic results will take six to eight weeks.
King and Williams say the associates are medically unlicensed, but were seen giving medications, fluids and foreign substances to the musician that were then locked away.
The women say "King was sequestered from all family members" the week prior to his death, and that Toney and Johnson were the only people with him.
Bryson disputed the allegations, saying King had the best treatment possible from three doctors and 24-hour-a-day monitoring from three nursing assistants.
"When the true facts come out, I'm absolutely confident this will go away," Bryson said.
The daughters' lawyer, Larissa Drohobyczer, provided the affidavits to CNN, but wouldn't comment on the case. King and Williams also refused to comment.
CNN has not received comment from Johnson or his attorney.
The Las Vegas Police said Tuesday the investigation will only move forward if the coroner's office finds in the full report that the death wasn't from natural causes.
The allegations are the latest salvo in a bid by some of King's children to wrest control of the late singer's assets, believed to be in the millions.
King had 15 children from several different relationships. Eleven children are still living.
Earlier this year, Patty King, Karen Williams and a third daughter, Rita Washington, went to court, accusing Toney -- the business manager -- of elder abuse and neglect. But a judge tossed out the case, for lack of evidence
In the weekend affidavits, Patty King and Williams requested a toxicology analysis or autopsy be conducted to determine the cause of their father's death.
On Sunday, the singer's body was shipped from mortuary to the coroner's office.
"The family has made some allegations. I can't go into specifics," Fudenberg told CNN. "We were contacted by several of the family members' legal counsel. They were making allegations of foul play."
A public viewing for the musician is scheduled for Friday at the B.B. King Museum in Indianola, Mississippi. Funeral services are set for the following day.
"Our investigation will not prohibit or delay the services they have planned," Fudenberg said.