Switzerland narrowly voted for the unspecified curbs in early 2014 with implementation to be made before February 2017.
The issue is newly topical as Europe faces its worst refugee crisis since the Second World War and Britain seeks migrant restrictions of its own to stay in the EU.
Swiss Federal President Simonetta Sommaruga said after talks in Brussels with European Commission head Jean-Claude Juncker that both sides wanted an accord but it was easier said than done.
"We have cleared the ground but we have no solution . . . there is still a difficult way to go and a lot of work to be done," Sommaruga told reporters.
"We might succeed, we might not."
Juncker said it was in the interests of both sides to find agreement.
"We hope that by February we will be able to set out what progress has been made," he said.
"We are confident of reaching an agreement."
The Swiss vote in February 2014 jeopardized years of close ties with the 28-nation European Union, which is founded on the core principle of free movement for all its citizens.
Switzerland is not an EU member state but it signed the Schengen agreement, agreeing to become part of Europe's passport-free zone which has come under huge pressure as the migrant
crisis has deepened this year.
In February, the Swiss government presented legislation to try and reconcile voters' wishes with EU rules by allowing in migrants under specific exceptions to some of the restrictions.
Around 80,000 immigrants, most from the EU, have settled in Switzerland annually in the past few years and almost a quarter of its 8.2 million people are foreign nationals.