This comes as a doctor treating the gravely-ill leader admitted that they may have contributed towards his condition.
Israel's Haaretz newspaper said blood thinning drugs given to Mr Sharon after a minor stroke in December may have worsened an undiagnosed disease of the blood vessels in his brain.
The brain condition, known as a cerebral amyloid angiopathy, was only diagnosed after last week's massive stroke.
The newspaper said doctors believe the anti-coagulant drugs could have caused the brain haemorrhage.
The doctor, speaking to the paper on the condition of anonymity, admitted the administration of the drugs represents a "screw-up".
But medics have pointed out that CAA is difficult to diagnose and sometimes can only be detected following a brain haemorrhage.
Signs of life
Mr Sharon was able to breathe on his own and move his right limbs during tests, but doctors said it is too soon to assess the brain damage from his massive stroke.
"The prime minister's condition remains unchanged... Today doctors will continue treatment begun yesterday," said Hadassah hospital spokesman Ron Kromer.
While doctors say he has not yet opened his eyes, the fact that he can breathe unassisted is encouraging as it is the first sign of brain activity.
Mr Sharon was in an induced coma since suffering a stroke last week, followed by three operations.
"We carried out pain stimulus tests which involved pressure," said Professor Shlomo Mor-Yosef, director of the Hadassah hospital in Jerusalem where Sharon is being treated.
"In the stimulus, we noted that the prime minister, Ariel Sharon, slightly moved his right arm and right leg.
"It was a very clear reaction to pain. These movements changed and became more and more significant the more we lowered the sedation," he said.
The leader's response was accompanied by a rise in blood pressure, which Dr Mor-Yosef said was a positive response.
Sedated yet stable
After days of uncertainty, doctors have appeared more confident they can save his life but warn his condition will not allow him to return to his duties as premier.
The prognosis has left a political void for Israel and has raised concerns for the immediate future of the Middle East peace process.
Felix Umansky, the chief neurosurgeon in attendance on Mr Sharon, stressed the premier remains in a critical condition and said it will take a few days for the damage to his brain to be assessed.
Doctors said they will continue reducing the level of sedatives over the next few days.
’Business as usual’
With Mr Sharon in intensive care, his stand-in Ehud Olmert has pledged business as usual, as public figures urge a time of national unity.
Mr Sharon's passing from politics will also leave stranded his new Kadima party that had been on course to emerge the largest player after an early general election fixed for March 28, although polls have still given it strong leads.
Israelis and world leaders have already braced themselves for the end of the Sharon era, fearing his demise would spark new turmoil in a region struggling to find the path to peace after decades of conflict.
One of Mr Olmert’s challenges will be the handling of this month's Palestinian parliamentary elections in which Islamic militant group Hamas is fielding candidates for the first time.
The Palestinians have expressed fears about the impact of a vacuum in Israeli politics but their leader, Mahmoud Abbas, said he did not expect a radical shift in Israeli policy with the exit of Mr Sharon.
Israeli Defence Minister Shaul Mofaz announced on Monday that the government had agreed in principle to allow Arab residents of East Jerusalem to vote.