Poland's Foreign Minister Radoslaw Sikorski was at the centre of negotiations between the Ukrainian government and opposition leaders.
Earlier in the day, the diplomat was overheard telling a Ukrainian opposition leader: "If you don't support this [deal] you'll have martial law, you'll have the army. You will all be dead."
He later told ITV News' Europe Editor James Mates that martial law in Ukraine was a "real possibility" and interior troops were being "readied" up until an agreement was signed.
The foreign minister told ITV News: "Well, as you can see it's almost miraculous. Within minutes of the agreement being signed the riot police are leaving."
The EU-brokered deal concluded that Ukraine will hold an early presidential election and will return to its 2004 constitution with reduced powers for President Yanukovich.