Electoral polls show that the Democratic Unionist Party and Sinn Fein will be "neck and neck" in the March Stormont election, Arlene Foster has claimed.
The DUP leader warned that a victory for Sinn Fein would give the party and Gerry Adams a "hugely significant worldwide propaganda boost".
Launching her party's seven-page manifesto Mrs Foster added that a win by Sinn Fein - the DUP's former powersharing partners - would threaten economic recovery, lead to a "divisive and destabilising" border poll and allow Sinn Fein to "shape policy consistent with Gerry Adams' all-Ireland agenda in a thousand different ways".
She added: "It would give Gerry Adams and Sinn Fein a hugely significant worldwide propaganda boost just months after nationalism's worst election since 1993 and would undermine the unionist confidence which is being rebuilt after so many years in decline.
"Our job is to make sure that does not happen."
Mrs Foster was too ill with the flu to take any questions from the media.
Before she began her speech at the manifesto launch in Belfast's Stormont Hotel Mrs Foster said she had "man flu".
A DUP spokesman later told the media she was not well enough to take questions.
A large portion of Mrs Foster's speech referred to Sinn Fein and Mr Adams.
She mentioned Mr Adams 12 times.
She criticised Ulster Unionist leader Mike Nesbitt's intention to transfer his vote to the SDLP, saying unionists transferring to nationalists will make it "much more likely that Sinn Fein win the election".
Following the election on March 2 there will likely be a lengthy period of negotiations between the political parties.
Mrs Foster said she will lead her party, along with deputy leader Nigel Dodds, into these negotiations.
The talks will include the divisive issue on how to deal with the legacy of troubles in the North.
Mrs Foster insisted the party will not permit "the rewriting of the past or the persecution of the security forces".
She said: "In this new political era, we will defend those who defended us through the dark days of the Troubles."
However, this will lead to further tensions with Sinn Fein and the SDLP who have both said soldiers must be held accountable under the same laws as the rest of the population.
Mrs Foster also said the DUP will oppose any Border Poll outside the terms of the Belfast Agreement.
"As we have seen from Scotland, in the absence of any likely change in the status of Northern Ireland, a referendum on our future constitutional position would be divisive and damaging," she said.
The DUP leader added: "We will honour all previous commitments we have made on the basis that republicans will honour theirs as well.
"Even after this unnecessary and damaging election, we will stand over the commitments that we have made in the past to help ensure politics works and people have confidence moving forward."
Stormont's institutions collapsed in January after serious flaws were uncovered in a botched renewable heat incentive (RHI) scheme, which could cost taxpayers £400 million.
A snap election was called after Sinn Fein's Martin McGuinness resigned as deputy first minister in protest at the DUP's handling of the RHI scandal.
Mrs Foster claimed Sinn Fein "precipitated a crisis" so they could deal directly with the UK government because the party is unable to deal with the DUP in negotiations.
She did not mention the RHI scandal in her manifesto speech.
However, she did say during post-election negotiations the DUP will "respond positively to any proposals to increase transparency, accountability and to help the institutions function more effectively".