New roadblocks were erected in northern Kosovo early Thursday, amid growing tensions and signals that Pristina was preparing to assert its authority over the Serb-dominated enclave, according to dpa. Serbian national television RTS reported that several trucks and tractors were parked on the road between Kosovska Mitrovica and Zvecan, blocking traffic. Another roadblock appeared in the largest Serb enclave in mainly Albanian Kosovo, on a main road in the northern village of Rudare, B92 news reported online. The barricades came up hours after Kosovo's prime minister, Hashim Thaci, said his government would appoint customs officials at contested border crossings in the Serb enclave on September 16. That is when a European Union-facilitated agreement between Serbia and Kosovo on customs comes into effect, aimed at ending a trade row and opening up the borders to goods from both sides. Tensions were heightened in July, when Kosovo sent police to take control over Jarinje and Brnjak, the two border checkpoints, to enforce a trade ban in response to an effective embargo by Serbia. Serb crowds blocked the main roads in the north and demolished the Jarinje checkpoint. One Kosovo policeman was killed. NATO peacekeepers in Kosovo, KFOR, took control of Jarinje and Brnjak, but in line with the agreements between Belgrade and Pristina, KFOR was due to pull out from the checkpoints on September 15. Despite pressure from Belgrade and the international community, Kosovan Serbs rejected the agreement and promised to resist its implementation. Kosovo declared independence from Serbia in 2008, but Serbia refuses to acknowledge it. It has also remained unable to assert any authority over the Serb-dominated north. The EU has demanded that Serbian President Boris Tadic sever political and financial support to the Serb resistance to Pristina's rule in northern Kosovo. Following that demand, voiced by German Chancellor Angela Merkel in Belgrade in late August, Thaci said his government would finally assert control over the north. Serbia's chief negotiator with Kosovo, Borislav Stefanovic, warned Wednesday that Thaci's promise of a move in the north is "unilateral action that can further destabilize" the already volatile area.