The 160 new cases follow Sunday’s 123, and shows a growing resurgence of the virus in Scotland.
Ms Sturgeon said the rising figures have given her “a greater sense of anxiety today” than at any time “probably for the last couple of months”.
While speaking during the daily coronavirus briefing, she revealed an incident management team is assessing a cluster of 22 cases in Ayrshire and Arran.
The team believe the incident appears “to be linked to indoor gatherings that took place the previous weekend”.
Nicola Sturgeon news: The First Minister has admitted ‘anxiety’ over Scotland’s rising coronavirus cases
Nicola Sturgeon news: Monday saw 160 new cases of the virus, which has not been reached since May 16
Ms Sturgeon also spoke about a spike in cases in Greater Glasgow and Clyde, which has seen 69 new cases yesterday.
She claimed the case spike “seems to reflect a number of small clusters, rather than one or two more significant outbreaks”.
But she also said no deaths linked to the virus have reported for just under a week.
Scotland’s deaths from COVID-19 remain at 2,494.
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Nicola Sturgeon news: Clusters of cases have been identified in Glasgow, Clyde, Ayrshire and Arran
Nicola Sturgeon news: Ms Sturgeon warned lockdown measures may be reinstated in Glasgow over the cases
The First Minister said at the briefing she believes the “quite high” new cases were in part “a result of greater numbers of people being tested”.
She also added proportionally, less than one percent of coronavirus tests in the country are positive.
But she also said: “The number of cases we are seeing right now is a reminder to all of us the virus is still a very real risk, it is a development that concerns me and it is one we are taking very seriously.
“I feel a greater sense of anxiety today than I have done any time probably for the last couple of months.
“We are in a fragile position – we have substantially lifted the lockdown restrictions, but in doing so we’ve allowed this virus opportunities to spread.”
Ms Sturgeon also warned Glasgow it could face a return of lockdown restrictions, which were lifted on July 10, if cases continue to rise.
She warned the areas seeing a surge in cases would be closely scrutinised, and confirmed the government were looking into whether “specific action” might be needed.
The SNP leader added: “As you’d expect, we are paying particularly close attention to Glasgow and Lanarkshire, and considering whether any specific action there may be required.”
At the start of August, Ms Sturgeon and Scottish authorities placed Aberdeen back under emergency measures.
Nicola Sturgeon news: Scotland has seen no deaths from the virus in just under a week
Nicola Sturgeon news: Lockdown restrictions were lifted in Scotland on July 10
Scottish opposition politicians have urged the First Minister not to be too hasty in reimposing “draconian” lockdown measures.
Scottish Labour health spokesperson Monica Lennon said: “It is deeply worrying that Nicola Sturgeon says she is feeling a high level of anxiety.
“The First Minister needs to not be hasty, and to consult a wide range of scientific experts before making any decision to reimpose draconian restrictions.
“We are in a position where the economy is incredibly fragile and restrictions on socialising could harm the most vulnerable in society.
“Now is a time for cool heads and Ms Sturgeon must be careful to base any decisions on the best evidence.”