Donetsk , Ukraine ( CNN ) -- Five militants were killed in the volatile eastern Ukrainian city of Luhansk on Monday after they took part in a large coordinated assault on a border guard base , an official at the Ukrainian State Border Guard Service told CNN . Also Monday , the White House announced Vice President Joe Biden would lead a U.S. delegation to Ukraine to attend the inauguration of Petro Poroshenko as president on Saturday . The attacks in Luhansk began early Monday when least 100 militants tried to storm the border unit on the southern edge of the city , said Oleg Slobodyan , the spokesman for the Ukrainian State Border Guard Service . The guards repulsed the first few attacks , but then the militants changed positions and began to shoot from inside nearby buildings where local people live , Slobodyan said , adding that the attackers were n't letting residents out of their homes . He said border guards were refraining from returning fire because they did n't want to cause civilian casualties . As of 9 a.m. local time ( 2 a.m . ET ) , an estimated 500 militants were still attacking the base , Slobodyan said . Fighters observed a roughly 20-minute truce in the afternoon for the removal of injured militants and border guards , the border service 's website said . Five militants were killed and eight were wounded in the fighting , Slobodyan said . Eight border guards have also been wounded in the fighting , Slobodyan said . It was not immediately possible to independently confirm the casualty numbers . Video from the scene shows at least one rocket landing on the edge of the compound . The separatist unrest that has gripped Ukraine in recent weeks has been centered in the eastern regions of Donetsk and Luhansk . Ukraine 's military sent air support for the border guards Monday , but residents ' proximity to the guards ' base `` limits the full-scale use of the military aviation , '' said Vladislav Selezhnev , a spokesman for the Ukrainian government 's Anti-Terrorist Operation . Still , the military was able to take out two mortar sites from the air , he said . Meanwhile , seven people were killed Monday by an explosion at the regional government building in Luhansk , health officials said . Journalist Victoria Butenko contributed to this report .
NEW : U.S. Vice President Biden to attend inauguration for new Ukrainian president . NEW : Two people die in explosion in government building in same city . No militants have been killed , the Ukrainian Border Police official says . The militants are shooting from nearby residential buildings , the official says .