The Scottish First Minister and SNP leader said that she did not think Labour's leader Jeremy Corbyn was "credible as an alternative prime minister".
The SNP would "look to be part of a progressive alliance" at Westminster if the General Election results in a hung parliament, Nicola Sturgeon said.
The SNP won 56 of the 59 seats in Scotland in the 2015 general election, and in the run up to that ballot Tories across the United Kingdom sought to raise fears about the impact a possible coalition between Labour and the SNP could have.
Polls show the SNP is set to easily win in Scotland in June, though May's Conservatives are expected to take some seats from them as the issue of keeping the United Kingdom together takes center stage. Scots rejected independence by 10 percentage points in 2014 and support for secession since then is little changed.
With less than two weeks before the vote, Sturgeon will set out her party's election plans in Perth, in central Scotland, on Tuesday, after postponing the event following the terrorist attack in Manchester.
The Daily Mail and The Times report Mrs May's attempt to relaunch her campaign following the damaging U-turn on social care by focusing on her policies to tackle domestic violence.
"In politics positions quickly become unsustainable and we have seen in the last few days ... this is not a prime minister who is very good at holding positions under pressure". "Now, more than ever before, we need strong SNP voices to stand up to the Tories, and stand up for Scotland, at Westminster", Sturgeon said.
Sturgeon, who said she wants an independent Scotland to be a full member of the European Union, argues that a new choice is needed because Scots voted to stay in the bloc in a referendum last June, at odds with the overall vote to leave. Scotland voted to stay in the European Union a year ago.