Peter Robinson said that it was too early to know if a deal could be reached
A second day of political talks aimed at averting the collapse of devolved government in Northern Ireland are under way at Hillsborough Castle.
The talks between Sinn Fein and the DUP are being chaired by the British and Irish prime ministers.
They are being held in an attempt to find agreement on the devolution of policing and justice powers to NI.
Speaking before the talks, DUP leader Peter Robinson said his party would not be pushed into a deal.
However, he added that his party was there for the "long haul".
"The issue of policing and justice has dogged us in the assembly," Mr Robinson said.
"It has taken away the focus that we should have on other issues."
"As well as setting a date for the transfer of security responsibilities from London to Belfast, there is also the question of the adjudication of controversial loyal order parades in dispute with Sinn Fein."
The Sinn Fein delegation attending the talks is led by Sinn Fein President Gerry Adams and deputy first minister Martin McGuinness.
Mr Brown and Mr Cowen arrived in Belfast on Monday and held late night discussions with both parties.
The leaders also held private talks on Tuesday morning before a meeting with the parties.
Speaking after Monday night's meeting broke up, a Downing Street spokesman said the talks were "hard going".
Mark Simpson, BBC Ireland correspondent
There's no prospect of a return to full-scale violence, but there is a full-scale political crisis.
The arrival in Northern Ireland of the two prime ministers is a sure sign that trouble is brewing. The blunt reality is there's no sign yet of any progress being made in the talks.
The equation is pretty simple - no deal means no devolution.
If these talks don't succeed, it's difficult to see how the Stormont Assembly will survive.
Sinn Fein and the Democratic Unionist Party - Northern Ireland's two biggest political parties - have been arguing for months over the transfer of policing and justice powers from Westminster to Stormont.
Sinn Fein wants the completion of devolution to happen as soon as possible, but the DUP argues there must be unionist "community confidence" before powers are put in the hands of local politicians.
The "confidence" issue causing most division is over the handling of parades.
The DUP wants to scrap the Parades Commission, which puts conditions on some of the most contentious marches, but Sinn Fein has accused the party of giving the Orange Order a talks veto.
On Tuesday, Sinn Fein minister Conor Murphy insisted the crisis was real, rejecting DUP claims that Sinn Fein had contrived it.
Sammy Wilson, DUP: "This is a contrived crisis"
Mr Murphy said: "It's not a contrived crisis. If it was contrived, I doubt that you would have the taoiseach (Irish prime minister), the British prime minister and the possibility of the Americans becoming involved."
Mr Murphy said the US government was keeping a close watching brief and US Secretary of State Hillary Clinton had spoken to people involved in the discussions.
It is understood that late on Monday night the two governments held private meetings with DUP and Sinn Fein negotiating teams, while senior figures from the other parties were briefed on progress.
The Ulster Unionists, the SDLP and the Alliance Party were also at Hillsborough Castle.
'Sword of Damocles'
Ulster Unionist leader Sir Reg Empey, speaking as he left the talks, said the two prime ministers were making a "big effort".
"They wouldn't be here if they didn't think the situation was serious, but equally we have been here before," he said.
"I have to stress conducting negotiations with the sword of Damocles hanging over your head is not the best way to do business."
SDLP deputy leader Alasdair McDonnell said that aside from the issue of policing and justice the governments should address the "dysfunctionality" of the Northern Ireland Executive.
The leaders cannot agree over the transfer of police powers to Stormont
Traditional Unionist Voice leader Jim Allister, who opposes power-sharing with Sinn Fein, said the need for the talks at Hillsborough showed the system of government in Northern Ireland was not working.
"What they've got is a rigged perversion of democracy which can never work because it is built on the empowerment by veto of a party, IRA/Sinn Fein, determined to prove Northern Ireland a failed political entity," he said.
Mr Brown has postponed Tuesday's cabinet meeting until later in the week.
Talks between the DUP and Sinn Fein had intensified in recent weeks, before collapsing in acrimony last week.
If Sinn Fein were to decide Martin McGuinness should resign as deputy first minister, the joint nature of the roles of first and deputy first ministers would mean that DUP leader Peter Robinson would also be forced out of office, collapsing the executive.
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