Ukraine's Interior Ministry on Tuesday accused the pro-Russian insurgency of attempting to procure white phosphorus ammunition, whose use is limited by international agreements.
The ministry cited intercepted conversations between the insurgents, who allegedly spoke about obtaining phosphorus missiles for Grad missile launchers at their disposal.
The rebels wanted to use the phosphorus missiles against civilians and blame it on the Ukrainian army, the statement on the ministry's website said.
The ministry did not release any intercepts, but said it would provide them to the United Nations and the OSCE.
The report did not specify the prospective source of phosphorus or say whether the rebels succeeded in procuring it.
Russian media said last month that the phosphorus bombs were used by Ukrainian army units battling the insurrection in eastern Ukraine.
White phosphorus is a highly flammable substance whose use against civilians is banned by the 1980 Convention on Certain Conventional Weapons, signed by both Russia and Ukraine.
Russia is routinely accused of providing arms to rebels, but official Moscow has denied it.