Viktor Yanukovych, who fled Ukraine in February, said he will try to persuade Russia to return Crimea to Ukraine.
During his first interview since fleeing to Russia, Yanukovych said the takeover is a tragedy that wouldn't have happened if he had stayed in power.
He added he still considers himself the legitimate president of Ukraine.
"I have the responsibility of the president of Ukraine, who was elected by the people. It doesn't matter how this looks, and no matter what I said - I cannot accept this, I will never accept this," Yanukovych said.
Ukraine and the West condemn Russia's annexation of Crimea last month as illegal.
Meanwhile, earlier this week Congress approved $1 billion in aid to Ukraine. President Barack Obama will sign the bill Wednesday providing the aid in loan guarantees.
"The president will continue to build support for the Ukrainian people at this critical time," White House press secretary Jay Carney said in a statement.
In addition to helping the cash-strapped country, the measure, approved by the House Tuesday in a 378-34 vote, is also meant to punish Russia for its annexation of Crimea.
Ariel Cohen, an expert on Russian and Eurasian affairs at the Heritage Foundation in Washington, suggested that while the loan package was a good start, more needed to be done.
"It doesn't resolve the problem, which is that Ukraine does not generate enough growth and income to plug the budgetary holes created by energy dependence on Russia," Cohen said.
Meanwhile, NATO's foreign ministers called on member nations to end civilian and military cooperation with Russia and instructed military leaders to quickly find ways to better protect countries that feel threatened by the Kremlin.