NI Secretary Peter Hain has urged the leadership of the republican movement to support the police.
Sinn Fein has been urged to support the PSNI
Mr Hain said they should make the move even if they could not sign up to policing structures.
Sinn Fein have said they have set out "very clearly" what needs to be done for them to back policing.
Mr Hain told BBC Radio Ulster on Monday: "Sinn Fein locally, on the ground, ought to take their obligations now seriously.
"To meet the requirements of the rule of law, co-operating with policing on practical issues that their communities increasingly expect them to do."
Speaking at the Magill Summer School in Donegal on Sunday Mr Hain had said that the PSNI and the government wanted to meet Sinn Fein this autumn for "mature and sustained dialogue" on policing.
Mr Hain said: "There is no reason to delay this engagement on practical issues."
He said republican communities desperately needed a police service to tackle crime and anti-social behaviour.
"Only the PSNI can deliver this service, and they can only deliver it in partnership with the community."
Mr Hain said he recognised that republicans had reservations about the police based on past experience.
However, he said they should appreciate the "sheer depth of hurt" felt by unionists and the police themselves about the past, and their suspicions about republican involvement in policing.
"The PSNI want to engage in this dialogue - indeed, increasingly are doing so, not least in County Derry and in south Armagh - and I hope that increasingly Sinn Fein will promote that," he said.
Peter Hain wants dialogue on policing
"Senior Sinn Fein figures in dealing with the PSNI over recent parades and their very significant efforts to bring about a peaceful summer on the streets has been encouraging."
The secretary of state said he remained optimistic that the issue could be resolved.
Sinn Fein President Gerry Adams accused the secretary of state of "patronising republicans".
He said republicans did support the rule of law and that Mr Hain's speech was both "inappropriate and an understatement".