Nikolic warned that Serbia will defend "every inch of its territory", including its former province of Kosovo where ethnic Serbs allegedly are under threat from Kosovar Albanians.
"Yesterday, we were on the verge of clashes", Nikolić said after he met with Serbia's top security body.
Nikolić accused Albanians of "wanting war" and said he's willing to send troops to Kosovo.
The two states have been embroiled in on-going tensions since Kosovo declared independence from Serbia in 2008 after a violent struggle.
Serbia retains effective control of the northern part of Kosovo, which is home to 40,000 to 50,000 Serbs who do not see Pristina as their capital.
Kosovo's deployment of special police forces to block the train line "showed that the Albanians want war", he said, before adding: "We are a country that must protect its people and territory".
Bitterness between Balkan neighbors flashed to the surface this weekend after a train was turned back from the Kosovo border.
Serbian Prime Minister Aleksandr Vucic then ordered the train to stop in the Serbian town of Raska, says the BBC, alleging that those forces meant to destroy the track.
DOJ Release Report on Reform Efforts By the Philadelphia Police Dept.
The Philadelphia Police Department requested the federal probe in 2013. The report's likely to call for more reforms. Van Dyke is facing trial on murder charges.
Serbian prime minister Aleksandar Vucic said he ordered the train to stop before reaching Kosovo's border.
Mustafa told reporters police forces along the border were deployed to prevent the train from crossing the border because the nation won't accept "machines that will provoke with a message of occupation".
"The introduction of an illegal rail service represents interference which threatens our sovereignty and proves Serbia is seeking to destabilise Kosovo", said Edita Tahiri, who leads Kosovo's negotiating team with Belgrade.
Nikolic also slammed the outgoing Obama administration, and the USA support of Kosovo's independence - comments that reflected the general presumption here that President-elect Donald Trump will be more favorable toward Russian Federation and Serbia.
Numerous remaining Serbs in Kosovo live around Mitrovica.
Tensions with Serbia were already running high, after former Kosovan prime minister Ramush Haradinaj was arrested in France on 5 January.
Normalizing relations between Kosovo and Serbia is key condition for both countries to progress towards membership in the European Union both governments are aiming for.
- Winter Weather Advisory Issued for the Possible Strong Winter Storm This Weekend
- Fresh prison riots in Brazil claim 10 lives, 3 inmates decapitated
- Coen brothers make TV switch with western
- West Ham won't be bullied in Payet saga
- Protesters at Women's March may outnumber those attending Trump inauguration
- Birmingham Civil Rights District Named National Monument
- Mediators fail to reach deal on Gambia crisis
- Bumblebee becomes the first endangered bee in continental US
- Baby kidnapped from Jacksonville hospital found alive 18 years later
- Patna: 17 killed as boat returning from festival capsizes in Ganga river