The draft, affecting able-bodied men between the ages of 18 and 25, is the latest indication that the Ukrainian conflict is rapidly intensifying.
Previous attempts at mandatory conscription have led to protests.
But during a meeting with the council Thursday, Poroshenko urged his countrymen to “keep a cold mind” as Ukrainians geared up for a broader conflict.
NATO has provided satellite images that appear to show Russian armored vehicles fighting in Ukrainian territory, CNN reports.
British intelligence says it has similar evidence, while U.S. officials say there are now up to 1,000 Russian troops in Ukraine.
On Friday, Russian President Vladimir Putin appeared to taunt Kiev by calling on separatist forces to open a humanitarian corridor in southeast Ukraine so that demoralized Ukrainian troops could flee home to their “mothers, wives and children.”
He also claimed that “a large number” of Ukrainian troops were not “in the military operation of their own volition” but were simply “following orders.”
Vox reported that in his statement Putin referred to Ukraine’s embattled Donbass region by the politically loaded term Novorossiya, literally “New Russia.”
Novorossiya is the old czarist name for the parts of Russia and Ukraine around the Black Sea and is a designation favored by separatists wishing to confer a historical integrity on the areas for which they are fighting.
“A counterfactual equivalent might be if a disturbingly post-Gestapo government in Germany began referring to the Netherlands as Western Germany or to western parts of the Czech Republic as Sudetenland,” John Besemeres, professor and adjunct fellow at the Australian National University’s Center for European Studies, tells TIME.
Responding to the incursions, Western envoys lambasted Russia on Thursday at an emergency meeting of the U.N. Security Council in New York City.
The U.S. representative, Samantha Power, said “Russia has come before this council to say everything except the truth. It has manipulated. It has obfuscated. It has outright lied. So we have learned to measure Russia by its actions and not by its words.”
The British envoy Mark Lyall Grant described Moscow’s incursions as a “brazen” violation of the U.N. Charter and international law.
Moscow’s U.N. envoy Vitaly Churkin admitted there were Russians fighting in the Ukraine but claimed they were volunteers.
He then went on to raise questions about the presence of U.S. military advisers in the country.
“A message must be sent to Washington — stop interfering in the internal activities of sovereign states and restrain your geopolitical ambition,” Churkin said, according to a U.N. statement.
Earlier on Thursday, U.N. Secretary-General Ban Ki-moon expressed alarm about the escalating conflict and urged Moscow and Kiev to follow up on talks held in Minsk earlier this week to forge “a peaceful way out of the conflict.”
Reports have meanwhile surfaced that separatist forces have succeeded in opening a third front after seizing the port city of Novoazovsk on the Sea of Azov in the wake of days of shelling.
Analysts continue to speculate whether the move is designed to draw troops away from heavy fighting near the separatist strongholds of Donetsk and Luhansk, or is part of a strategic maneuver to forge a corridor to the Russian-controlled Crimean Peninsula farther west.