BRUSSELS - The EU welcomed Ukraine into the Western fold Friday, signing the political provisions of a landmark accord as a defiant Russia formally completed its takeover of Crimea.

Seeking some leverage over a newly-assertive Moscow, European Union leaders agreed sanctions against top Russian politicians and stepped up efforts to cut the bloc’s debilitating energy dependence on Russia.

Signing the Association Accord “symbolises the importance both sides attach to this relationship... and the joint will to take it further,” EU president Hermann Van Rompuy told Ukraine interim premier Arseniy Yatsenyuk.

The EU was offering Ukraine its “steadfast support,” Van Rompuy said, promising help to get the country’s struggling economy back on track. “We are sure that together we will succeed,” Yatsenyuk said after the European Union’s 28 heads of state and government signed the document.  At another ceremony, this time in Moscow, President Vladimir Putin signed the documents making Crimea part of Russia. “Today we have a serious, momentous event,” Putin said. “I want to congratulate you, all the inhabitants of the country, Russian citizens, the inhabitants of Crimea and Sevastopol on this landmark - without any exaggeration - event.”

The annexation of Crimea, after a referendum Sunday condemned as illegal by Washington and Brussels, prompted both to impose sanctions on Russia.

US President Barack Obama blacklisted 20 Russian lawmakers, senior government officials and businessmen, in addition to 11 already targeted, and warned Moscow it faced international isolation if it did not reverse course.

Moscow responded in kind, announcing sanctions of its own against nine US officials, including top political figures and presidential aides. After long talks in Brussels, EU leaders hit 12 more Russians with travel bans and asset freezes, bringing their list to 33. Among them was Russian Deputy Premier Dmitry Rogozin, also targeted by Washington and who vehemently dismissed the measures. “All these sanctions aren’t worth a grain of sand of the Crimean land that returned to Russia,” Rogozin said in a tweet. Putin also made light of the sanctions, joking that he would open an account with a bank on the Washington blacklist.

EU leaders also agreed on the need to fast-forward plans to cut the bloc’s energy dependency, notably on Russia which supplies more than a quarter of its natural gas, much of it in pipelines through Ukraine.

“Reducing our energy dependency, especially in relation to Russia, was a key topic” at the two-day summit, Van Rompuy said. “If we dont take action now, by 2035 we will be dependent for 80 percent of oil and gas,” he warned. Many EU nations are heavily reliant on Russian energy and so the bloc is divided on how far it can go with economic sanctions. United Nations Secretary-General Ban Ki-moon said on Friday the Ukrainian crisis could only be resolved through a diplomatic solution that respected the territorial integrity of the splintered ex-Soviet state.

Ramping up the pressure further, Moscow demanded that Ukraine pay back $11 billion it had supposedly saved because of the discounted gas price.

“The Ukrainian state saved some $11 billion dollars and accordingly the Russian budget has a missed profit of the same $11 billion,” Prime Minister Dmitry Medvedev said.

The economic fallout from the Ukraine crisis continued when Fitch joined fellow ratings agency Standard & Poor’s in downgrading Russia’s credit outlook from stable to negative because of the growing risk of Western sanctions.

“Since US and EU banks and investors may well be reluctant to lend to Russia under the current circumstances, the economy may slow further and the private sector may require official support,” Fitch said.

The International Monetary Fund said meanwhile it had made “significant progress” in talks with Kiev over the resumption of a vital support programme. Japan also plans to provide nearly $1.0 billion in aid to Ukraine, reports said, while the EU has announced funding of 11 billion euros ($15 billion) in all.

On the ground in Crimea, Russia continued to consolidate its position, with Kiev preparing an evacuation plan for thousands of Ukrainian soldiers and their families based there.

Kiev fears Moscow may venture into Ukraine’s eastern half of the country, home to a large Russia-speaking population, on the pretext of protecting Russian compatriots.

Yatsenyuk said earlier that Ukraine would “respond firmly, including through military means,” if Russia took that option but on Friday he put the stress on the need for economic sanctions.

A “military response is not acceptable... (that way we) have a third world war,” he said.

“The best way to contain Russia is to impose real economic leverage on them,” he said.

Washington said Thursday that Russian Defence Minister Sergei Shoigu had promised his US counterpart Chuck Hagel that Moscow would not move into eastern Ukraine.