Sanader made the statement when asked if Croatia would accept the expansion of the Central European Free Trade Agreement (CEFTA) with more favourable conditions for Serbia and if it was willing to make concessions to Serbia.
"What has been signed must be respected, we will insist on that also in case of other countries," the PM said.
He went on to say that after signing bilateral agreements countries should not make unilateral moves on the international scene because this was against international democratic standards.
Eight countries are involved in the negotiations and they must reach the best possible agreement on CEFTA which they will be able to back, he said.
"If not, there will be no agreement on CEFTA. It must be an agreement which all eight countries will be able to say they support it," Sanader told reporters after meeting Moldavian PM Vasile Tarlev.
The text of the agreement on the expansion of CEFTA was harmonised at multilateral talks in Brussels on Friday, with the exception of two minor sections at the request of the Serbian delegation, Croatia's chief negotiator and state secretary for the economy Vladimir Vrankovic told Hina.
The two sections refer to the revocation of customs duties on some products for which Serbia requested a three-year transitional period.
Vrankovic said the Serbs were given three weeks to settle the dilemmas at internal consultations and that the agreement on the enlargement of CEFTA was expected to be initialled on November 9 and signed in early December.
After Bulgaria and Romania leave CEFTA upon joining the European Union on January 1, 2007, Croatia and Macedonia would be joined by Bosnia and Herzegovina, Montenegro, Serbia, Albania, and Moldova. By joining CEFTA, these five countries would commit to behaving in accordance with World Trade Organisation rules.