"Serbia is continuing its interference and has a tendency to destabilise us," Sejdiu said in an address to parliament.
Sejdiu said "the mentality of conflict and hate is still present in the heads and institutions in Serbia". He added: "These destabilising policies of Belgrade do not help Serbs or the region."
At a meeting in Zvecan, just outside the ethnically divided northern town of Mitrovica, 80 Serbian lawmakers from Belgrade and 31 delegates from Kosovo's Association of Serb Municipalities adopted a declaration that denounced the territory's independence.
After the session, Slobodan Samardzic, a Serb politician from the nationalist Democratic Party of Serbia, said, "Kosovo hasn't moved an inch from where it was a year ago".
Police had increased their presence in Mitrovica.
Earlier on Tuesday, hundreds rallied against Kosovo independence in Serbia's second-largest city of Novi Sad. There were no major incidents.
Serbia's capital Belgrade, where embassies and businesses were attacked last year after Kosovo's secession, was calm, but police strengthened security around diplomatic missions.
Serbia and its huge ally Russia remain opposed to Kosovo independence, although it has been recognised by the United States and its key European allies.
On Monday, Serbia's President Boris Tadic told Reuters his country would never recognise Kosovo. "Serbia will never take a single action that implies Kosovo's independence," he said.
(EurActiv with Reuters)
