The European Union is putting pressure on Switzerland to start talks on new bilateral agreements, governing tax evasion and customs fraud. The EU's foreign affairs commissioner, Chris Patten, warned that any delay could seriously damage relations.
In what is being seen as a veiled warning to Switzerland, Patten hinted that a delay in new negotiations could hold up the ratification of seven bilateral accords agreed between Switzerland and the EU.
In a letter to the Swiss foreign ministry, he wrote: "Any further delay could have a serious negative impact on the future course of relations in these and other areas."
He added that a new round of talks "could only benefit" the process of ratifying the accords.
The seven agreements - governing issues such as transport and the free movement of people - were approved by Swiss voters last May, but some EU states have been slow to give their backing and final ratification is now not expected before the summer.
Responding to Patten's letter, the Swiss foreign ministry said it was entirely inappropriate for the EU to make ratification of the seven bilateral accords dependent on new negotiations.
"Any connection between the new negotiations and the on-going ratification of the bilateral accords, as suggested in this letter, is wholly unacceptable to us," said foreign ministry spokesman, Ruedi Christen.
Christen also made clear that while Switzerland was ready to discuss closer cooperation on security issues, it needed further assurances that its concerns were being taken seriously by the EU.
"We need a signal from the Council of Ministers, not just from the Commission," said Christen. "And even more importantly, all outstanding issues from the previous round of accords need to be settled."
swissinfo with agencies