Milanovic told the highest national law-making body that the country was in a serious situation while the government "is behaving unseriously".
He called on the PM to cease ignoring the parliament and come there.
"We do not insist on elections now, this is not Libya, but the PM must say when the elections will be held as this will defuse tensions," the SDP chief said.
Milanovic admitted that Croatia should first complete its European Union accession negotiations and then hold the elections but that they should be organised before December this year.
Speaking on behalf of the ruling Croatian Democratic Union (HDZ), Andrija Hebrang said that the SDP request about the elections was legitimate, adding that however, the polls would be organised after the completion of Croatia's EU entry talks.
"We accept your suggestion that the elections be held within a sensible time frame, but the sensible time frame is after the completion of the (EU) negotiations and it will depend mostly on us, on the Opposition and the entire Croatian political public... Therefore let's go together until the completion of the negotiations, Hebrang said.