Former Ukrainian Prime Minister Yulia Tymoshenko has said the Minsk process for resolving the conflict in eastern Ukraine has failed to produce results and needs to be accompanied by a parallel peace process based on the 1994 Budapest Memorandum.

In an interview in Brussels with RFE/RL, Tymoshenko said the Budapest document -- under which Russia, the United States, and the United Kingdom guaranteed Ukraine's territorial integrity in exchange for Kyiv's renunciation of nuclear weapons -- should be "the basis of diplomatic negotiations on the establishment of peace in Ukraine."

She criticized the government of President Petro Poroshenko for "forgetting" about the existence of that document.

Tymoshenko, who heads one of Ukraine's largest opposition parties and who is currently nearly even with Poroshenko in public-opinion polls for the 2019 presidential election, emphasized that "Ukraine and Russia are warring countries today" and "Russia is in a state of war against Ukraine."

After Russia annexed the Ukrainian region of Crimea in March 2014, Moscow began fomenting unrest in regions of eastern Ukraine. Since then, Russia has provided military, political, and economic support to separatists in parts of the Luhansk and Donetsk regions.

Moscow denies interfering in Ukraine's internal affairs, despite compelling evidence to the contrary.

Tymoshenko told RFE/RL that "the path to peace" lies through establishing a "completely different negotiation format" involving all the Budapest Memorandum signatories. There is no point, she said, in negotiating with the leaders of the Russia-backed separatist units, because "they are absolute marionettes."

At the same time, Tymoshenko said, Ukraine must step up its military response to Russian aggression "by every minute and every second strengthening our army."

She urged the United States to "enable Ukraine to acquire" high-tech defensive weapons.

Tymoshenko confirmed that her Batkivshchyna (Fatherland) party intends to contest both the parliamentary and the presidential elections scheduled for 2019.

According to a poll conducted this month, Tymoshenko had 14.4 percent support, compared to 16.1 percent for Poroshenko.