Prime Minister David Cameron "will bring together" French President Francois Hollande, Italian Prime Minister Matteo Renzi, German Chancellor Angela Merkel and Obama to hear Poroshenko, the source added.
"The meeting will provide leaders with the opportunity to hear President Poroshenko's assessment of the latest situation on the ground and his discussions with President Putin," the source said yesterday.
"It will also send a clear signal of their support for Ukraine's sovereignty and that the onus is on Russia to de-escalate the situation," the source added.
Ukrainian Prime Minister Arseniy Yatsenyuk said the proposal was meant to "pull the wool over the eyes of the international community".
Some 2,600 people have been killed in five months of fighting in eastern Ukraine between Ukraine's army and pro-Moscow rebels which the West suspects are supplied and trained by Russian and include Russian soldiers.