An all-Ireland police intelligence agency would be the most effective way to tackle criminals and paramilitaries, the SDLP has said.
Mark Durkan wants more north-south cooperation
The party made the call in a 24-page document entitled "North-South Makes Sense".
It also called for an all-Ireland criminal assets bureau and sex offenders register.
The document proposes closer health,
economic, farming, education, housing, environment and transport links.
SDLP leader Mark Durkan said unionists should not fear such cross-border cooperation.
"People who are unionist, nationalist or neither should have nothing to fear from dynamic north-south co-operation," he said.
"We are all losers without it."
The party said criminals who exploit different jurisdictions would be best targeted through all-Ireland mechanisms.
An all-Ireland intelligence agency would be staffed by officers from the PSNI and Garda, the party said.
However, the DUP has published a document calling for greater east-west cooperation between Northern Ireland and Scotland.
The party's MEP, Jim Allister, said the two countries had "well-documented and irrefutable historical links".
"The problems afflicting both countries are common, namely poor transportation infrastructure, the decline of heavy industry and textiles and an underdeveloped tourism potential," Mr Allister said.
"Bearing this reality in mind, the most obvious and natural area of cooperation is cooperation undertaken on an east-west basis, rather than the unnatural and politically-motivated north-southery."