KIEV, Ukraine - Ukraine's interim government took additional steps Tuesday to reassert its control by appointing a new military commander and shoring up security forces, even as some leaders made urgent calls for volunteers to take up arms against pro-Russian separatists in the eastern part of the country.

Amid reports of fresh violence, former Prime Minister Yulia Tymoshenko urged the creation of a "volunteer army" because neither Ukraine's army nor its security services have been effective in handling outbreaks of rebellion, the Russian news service Interfax reported Tuesday.

Hers was one of many calls to form combat-ready units of "self-defense" forces ahead of May 25 presidential and mayoral elections. Andriy Tiron, battalion commander of the National Guard, told reporters in Kiev that demonstrators who helped oust the previous pro-Russian government were being urged to volunteer for military duty. But there was confusion about who would command them and what their duties would be.

In a brief statement that appeared on his official website, the acting president, Oleksandr Turchynov, said Lt. Gen. Anatoly Pushnyakov has been appointed to take command of the army. The statement offered no further details. Turchynov also published a decree sacking the top regional administrator in Odessa as violence continued to flare around eastern Ukraine.

Late Tuesday, there were reports of fighting in the eastern coastal town of Mariupol. Interfax, the Russian news service, quoted a separatist representative as saying that Ukrainian forces had staged an attack. Local media reported cars ablaze and a skirmish underway near the Mariupol airport.

Earlier, in the Luhansk region, about 20 armed militants destroyed a military radar station, according to the website of southern Ukraine's prosecutor general. The report said the militants outnumbered Ukrainian soldiers at the installation and slipped away after the 4 a.m. attack. There was no mention of casualties. In perhaps another sign of the confusion and suspicions of mixed loyalties in parts of Ukraine, the prosecutor said there would be an investigation of the soldiers' conduct.