The Ukrainian Interior Ministry said earlier that Poroshenko will sign a decree announcing a temporary cease-fire soon.
In a statement posted on its website June 20, the Interior Ministry said under the cease-fire "terrorists can lay down their arms and those who will not do this will be killed."
Poroshenko visited a National Guard counterterrorism center on June 20.
He had been expected earlier to announce a 14-point peace plan.
According to an unofficial copy published by the media, the plan calls for the creation of a 10-kilometer buffer zone on the border with Russia.
"We have information that additional tanks departed from a deployment site in southwest Russia yesterday," a senior administration official told reporters in a June 20 conference call on condition of anonymity.
Ukrainian officials on June 20 briefed EU and G7 diplomats about additional military hardware that Kyiv claims Russia is providing to the separatists, the official said.
Some of the equipment appears to be materiel currently used by the Ukrainian military but not by the Russian military, which could allow separatists to falsely claim that they recovered the hardware on the battlefield and not from Russia, the official added.
The individuals are Valery Bolotov, the self-proclaimed leader of the "Luhansk People's Republic"; Igor Girkin (aka Strelkov), who commands the Donbas People's Militia; Valery Kaurov, leader of the Union of Orthodox Citizens of Ukraine; Sergei Menyailo, the acting governor of Sevastopol; Vyacheslav Ponomaryov, the self-proclaimed mayor of the city of Slovyansk; Andrey Purgin, a leader in the self-declared "Donetsk People's Republic"; and Denis Pushilin, the self-declared chairman of the Supreme Soviet of the "Donetsk People's Republic."
NATO Secretary-General Anders Fogh Rasmussen said on Thursday that at least a few thousand more Russian troops were now at the frontier, and called it a regrettable step backwards following an earlier withdrawal from the border.
"There has been no build-up," Yuri Ushakov, President Vladimir Putin's foreign policy adviser, told reporters.
He said Russia was concerned about security at the border and added: "This means just the border guards are getting a few reinforcements, and troops have been withdrawn."
On @lifenews_ru, batty MP Elena Mizulina declares Ukraine "accounts for 70% of child porn". HT @buu3a pic.twitter.com/D3aRJLj2t6
— Oliver Carroll (@olliecarroll) June 18, 2014
Spent time @ Army SOS in Kiev, grassroots initiative providing Ukr soldiers w basic eqipmt. Generals r still sending units 2 front w/o armor
— Oliver Carroll (@olliecarroll) June 20, 2014
I saw them take a dozen calls pleading for assistance. They say their main problem not money or ppl willing 2 help, but govt bureaucracy.
— Oliver Carroll (@olliecarroll) June 20, 2014
400 flak helmets being held up by Ukrainian customs, say Army SOS. (!)
— Oliver Carroll (@olliecarroll) June 20, 2014
Officials say Poltava pipeline explosion likely sabotage. Why? Gazprom set to bid on a part of Nord Stream on July 15 http://t.co/6rtXHrwFXM
— Isaac Webb (@isaacdwebb) June 20, 2014