Mr Adams claimed an “anti-agreement axis” combining Unionists, the Northern Ireland secretary Theresa Villiers, and Downing Street, was conspiring to undermine the deal.
The Sinn Féin leader accused British prime minister David Cameron of disengaging from the peace process in a way that encouraged the Democratic Unionist Party to be obstructive at Stormont.
Mr Adams said talks slated for next month to sort out issues related to flags, parades, and dealing with the legacy of thousands of conflict murders, were now unlikely to take place.
“The political process is in trouble. I believe that the political process faces its greatest challenge since the Good Friday Agreement negotiations in 1998. The anti-Good Friday Agreement axis within unionism; the pro-unionist stance of the British secretary of state Theresa Villiers; the refusal of Downing Street to honour its own obligations are combining to create the most serious threat to the political institutions in the North in recent years.
“The result of all this is directly undermining power -sharing and partnership government. The unionist leaderships have been encouraged in their posture by a British government that has not been fully engaged with the political process for four years,” Mr Adams said.
The Sinn Féin president accused unionists of failing to engage positively in recent political negotiations aimed at averting a repeat of last year’s communal violence.
Dialogue has been stalled in a unionist protest over the handling of a loyal order parade in north Belfast.
DUP leader Peter Robinson has said the Stormont institutions have been put under threat by a ruling barring an Orange Order parade from marching past Ardoyne.
Mr Adams claimed the DUP was unwilling to participate positively in any of the institutions.
“Instead it has adopted a tactical approach aimed at serving the political agenda of a fundamentalist rump in their party rather than the needs of the whole community,” Mr Adams said.
Relations deteriorated after last year’s summer of sectarian violence.
A proposal to develop a peace centre at the site of the Maze prison, where IRA hunger striker Bobby Sands died, was impacted upon last year when the unionists withdrew their support.
Mr Robinson said he was responding to victims’ concerns about the potential of a centre at the former prison being turned into a “terrorist shrine”.
Efforts were made to resolve community tensions via five-party talks chaired by former US diplomat Dr Richard Haass which ended after Christmas without agreement.