(Adds violence, quotes)
By Ellie Tzortzi
BELGRADE, Feb 17 (Reuters) - Serbia’s leaders pledged peaceful resistance after Kosovo’s declaration of independence on Sunday, but angry protesters turned to violence in Belgrade and a Serbian stronghold in Kosovo.
Some 2,000 people gathered at the U.S. embassy to vent their anger at American backing for the breakaway province.
"Kosovo is the heart of Serbia," many chanted as they ripped up paving stones and prised concrete and tiles from nearby buildings to throw at riot police along with bottles and flares. Several police and rioters were bloody and injured.
In the Kosovo Serb stronghold of Mitrovica, hand grenades were thrown at EU and U.N. buildings. One exploded causing no major damage.
Local news agencies also reported protests in Novi Sad in northern Serbia and in Banja Luka, capital of the Bosnian Serb Republic whose leaders look to Kosovo for a precedent they could use to try and secede from Bosnia.
In Serbia, political leaders were united in their anger at Kosovo’s declaration but gave out very different signals on how the move would affect Belgrade’s ties with the West.
Nationalist Prime Minister Vojislav Kostunica, who led a diplomatic battle to retain the region, attacked the United States and European Union for supporting the secession of a province Serbs see as their religious and historic heartland.
In a televised address to the nation minutes after Kosovo formally severed ties after nine years under U.N. control, he accused the United States of being "ready to violate the international order for its own military interests".
"As long as the Serb people exist, Kosovo will be Serbia," Kostunica said.
"The declaration by the false state under the tutelage of the United States and EU is the final act of the policy of force which started with the insane bombing of Serbia and continued with the arrival of NATO troops in Kosovo.".
The United States spearheaded the 1999 NATO air war that expelled Serb forces from the province to stop the mass killing of Albanian civilians in a counter-insurgency crackdown.
Kostunica said mass protests would be called soon.
PRESIDENT RULES OUT VIOLENT RESPONSE
Pro-Western President Boris Tadic, whose party is in a shaky coalition with Kostunica’s, called for calm.
"Serbia will never recognise the independence of Kosovo," but "will go through this peacefully, with dignity", he said in a statement. "Serbia will persist ... and defend its interests and international law, no matter how long it takes."
Russia, Belgrade’s strongest ally, called U.N. Security Council talks on Kosovo for Monday. Tadic was heading off to New York late on Sunday to attend the closed-door session which has no real chance of reversing Western backing for Kosovo.
Serbian Foreign Minister Vuk Jeremic will go to Brussels on Monday where EU foreign ministers will meet on Kosovo, which hopes most member states will swiftly recognise it.
Tadic favours separating the issue of Kosovo from Serbia’s long-delayed EU membership bid. But Kostunica insists Brussels must give up support of Kosovo if it wants Serbia as a member.
The staunchly nationalist Radicals, Serbia’s strongest party, called on Kostunica and Tadic to "channel the unrest and anger" of Serbs into a huge rally.
"As long as there are Serbs, we will go on fighting for Kosovo," their leader Tomislav Nikolic said.
The sharpest reaction was from the Serb Orthodox Church in Kosovo, whose leader Bishop Artemije denounced the army for doing nothing and said Serbia should buy arms from Russia to fight. (additional reporting by Ljilja Cvekic; editing by Richard Meares)