The approval of Serbia's new constitution reasserting its claim over Kosovo hinged Sunday on the turnout in the last hours of voting, with independent observers warning of nervousness on polling stations as the two-day referendum wound down, reported The Associated Press. The state Electoral Commission said the turnout by 6 p.m. (1700 GMT) was 47.03 percent Sunday, the final day of voting on the document whose key point declares Kosovo an «integral part of Serbia» despite ongoing U.N.-brokered talks on the province's future status. To be approved, the draft requires that a majority of Serbia's 6.6 million-strong electorate casts a «yes» vote for the charter. The Belgrade-based Center for Free Elections and Democracy, which earlier gave an estimated 41.9 percent turnout by 5 p.m. (1600 GMT), said it was «too low ... but not impossible» the referendum would succeed. The group's monitors also reported «increasing nervousness» by election authorities at polling stations. Prime Minister Vojislav Kostunica issued Sunday a final appeal on all voters «who hold Serbia in their hearts» to head to the polls and back the new constitution, warning of «unforeseeable consequences» if it is not voted in, the premier's spokesman Srdjan Djuric said. «Citizens, go out and vote 'yes,' for a better life for everyone,» Serbian President Boris Tadic said later in his own eleventh-hour plea. A massive government campaign in Serbia to say `yes' to the document continued into Sunday, with ads flashing at the top of television screens on the state-run broadcaster calling on people to vote in favor of the draft constitution. The draft is a 206-article document offered as consolidating democracy and the rule of law in the Balkan country. But the focus _ and the expected lure for Serb voters _ has been the preamble seeking to prevent a possible secession of the disputed southern province. Independence-seeking ethnic Albanians form 90 percent of the population in Kosovo, which has been under U.N. administration since 1999, when U.S.-led NATO air strikes halted a Serb crackdown on the separatists. The referendum has been strongly condemned by the ethnic Albanians, who have long boycotted any ballot under Serb auspices. The government in Belgrade did not even invite them to take part. Western diplomats have warned that only the international negotiations can decide on Kosovo's future, but the Belgrade politicians believe that adopting the new constitution would bolster their position in the talks. Serbs cherish Kosovo _ which today is home to a dwindling Serb community of 100,000 _ as their historic heartland.