Nicola Sturgeon today warned Covid lockdown rules could return to Scotland if a fresh "surge" continues.
The First Minister said the next few weeks are a "pivotal moment" after cases almost doubled in a week and the daily test positivity rate hit 14.5%, up from 12.4% the previous day.
Scotland has recorded 10 coronavirus-linked deaths and 4,323 cases in the past 24 hours, she announced.
Welsh First Minister Mark Drakeford also refused to rule out the return of restrictions, telling a press conference: "We have never said in Wales a move away from restrictions is a one-way street and there was never any turning back.”
Ms Sturgeon said: "If the surge continues and accelerates, and if we start to see a substantial increase in serious illness as a result, we cannot completely rule out having to reimpose some restrictions.
"Of course we hope not to have to do that and if we did, we would be as limited and as proportionate as possible.
"However... what happens in the next few weeks will depend... on all of us. This is yet another fragile and potentially very pivotal moment in our journey through this pandemic."
Meanwhile Ms Sturgeon confirmed Scotland's Covid public inquiry will start by end of this year - months earlier than the UK government's.
In an announcement, the First Minister said she will stand by an earlier pledge to get the inquiry under way before the end of 2021.
That is despite the UK government only pledging to start its inquiry in Spring 2022, claiming civil servants and ministers are too busy.
Aamer Anwar, solicitor for the UK-wide Covid-19 Bereaved Families for Justice, said: “Today is the first important step in establishing accountability for 10,421 lives lost to Covid-19 in Scotland.
“Boris Johnson should take note that his Government can no longer be allowed to hold the process back from asking difficult questions.
“There were 154,811 Covid-19 deaths in the UK, every single death represents failure and Public Inquiries cannot be delayed any longer by a UK Government, whether it be in England, Wales or Northern Ireland.”
Ms Sturgeon told a televised briefing: "We have this morning published draft aims and principles for the inquiry."
Following a consultation between now and end of September, including bereaved families, the Scottish government will publish formal terms of reference.
Bereaved families already fear the UK inquiry will be "kicked into the long grass" beyond spring 2022 after government lawyers told them the Health Secretary was “very busy”.
The families’ lawyers told the Mirror ministers have not begun drawing up terms of reference and have so far ignored their suggestions for the inquiry's scope.
Scotland's national clinical director Professor Jason Leitch said he and other public health advisers are "concerned" by a sharp rise in Covid-19 cases.
In the past week, case figures have more than doubled, from around 10,000 to more than 21,000.
"We are concerned," he said on BBC's Good Morning Scotland programme.
"It's principally young people, but not only young people.
"But a big percentage are under 40, so that means the harm is not as significant, but people are still harmed by this virus, either the older people who get it or some small proportion of those younger people."
Hospital figures have also stagnated in recent weeks, with the same number (356) in hospital on Monday as compared with the day restrictions were eased in Scotland, although the figure has risen from 312 on Friday, adding another 18 on Monday.
When asked about the possible return of restrictions because of the rising numbers, Prof Leitch said: "Cabinet will meet today and we've given balanced advice, we've told the truth about the state of the pandemic."
When asked if restrictions could be imposed as early as Tuesday, he said: "I don't expect us to make dramatic changes, I think we will almost certainly keep the baseline mitigations that we've got in place just now."
