BRUSSELS — Ukraine’s new president signed an economic and political pact with the European Union on Friday, pushing his troubled country closer into a European orbit over the protests of Russia, which warned of possible sanctions.

“What a great day!” a beaming President Petro Poroshenko said in Brussels. “Maybe the most important day for my country after independence” from the Soviet Union in 1991.

Russia has long been opposed to closer ties between Ukraine and the EU. Moscow is loath to see its historic influence wane in its strategic neighbor, which it considers the birthplace of Russian statehood and of Russian Orthodox Christianity.

“There will undoubtedly be serious consequences for Ukraine and Moldova’s signing,” Russian Deputy Foreign Minister Grigory Karasin said.

European Union leaders decided not to immediately impose new sanctions on Russia for destabilizing eastern Ukraine. But in a statement, they warned that new sanctions have been prepared so they could be levied “without delay” and listed several demands for Vladimir Putin’s government and the pro-Russian rebels in eastern Ukraine.

Poroshenko’s pro-Moscow predecessor, Viktor Yanukovych, had backed out of signing the agreement in November, igniting the bloody protests that toppled his government in February. Tensions between Ukrainians in the west who want closer ties to Europe and those who favor traditional ties with Russia sparked an insurgency in the east and Russia’s annexation of the mainly Russian-speaking Crimean Peninsula in March.