President Vladimir Putin on Saturday urged Ukraine to join forces with former fellow Soviet state Russia, saying Russians and Ukrainians were "one people."
The Russian president's remarks, made as he visited Kiev, highlight an ongoing tug-of-war Moscow has with Brussels over Ukraine's moves to seek closer ties with the EU.
In Ukraine to celebrate the 1025th anniversary of the arrival of Christianity in what was once known as Kievan Rus, a vast territory comprising modern-day Ukraine and Russia, Putin said the two majority Orthodox neighbours should further integrate economically.
"Intense competition is going on now in global markets, for global markets," Putin said after talks with Ukrainian President Viktor Yanukovych.
"Only by joining forces can we be competitive and win in this rather tough competitive fight."
"We have every reason to believe that we can and must do it," he said.
However he added that Russia would "respect whatever choice the Ukrainian people and the Ukrainian state will make".
The religious festivities come ahead of a November summit in Vilnius that could see the European Union sign a landmark trade agreement with Ukraine.
This would open up EU markets for Ukrainian exports. At the same time, the Kremlin has been pushing Kiev to join a Russian-led customs union.
In talks with Yanukovych, Putin said Russia was determined to forge a closer partnership with Ukraine, noting the two countries were facing "major, complex" problems.
Yanukovych said the two countries had "lots of mutual interests".
The talks were seen as a last-ditch effort by Putin to persuade Yanukovych to drop plans for closer ties with the European bloc.
The agreement with Brussels has been repeatedly postponed after a Ukrainian court jailed former prime minister Yulia Tymoshenko for seven years in 2011, triggering a dramatic deterioration in ties and making Kiev more vulnerable to the Kremlin's advances.
In a sign of continuing tensions, the European Union said Friday the "time was running out" for Ukraine to sort out a number of trade disputes if it wanted to sign the agreement.
Since coming to power in 2010, Yanukovych has performed a delicate balancing act by seeking closer European ties while also trying to remain on good terms with its prickly Soviet-era master, Moscow.
Russia has sought to keep Ukraine in its orbit but Kiev has steadfastly resisted pressure from Moscow, which wants to gain control of Ukraine's gas pipeline network.
Earlier Saturday, Putin, accompanied by Russian Orthodox Patriarch Kirill and Yanukovych, took part in a prayer service in Kiev.
Overlooking the Dnipro River, the park where the ceremonial prayer took place hosts a monument to Prince Vladimir the Great revered for converting ancient Rus to Christianity in 988.
As well as promoting economic ties, Putin also stressed the bonds between both countries forged by a common history and what he called Russia and Ukraine's "spiritual unity".
"Together we went through great trials, tribulations and tragedies, together we built and defended the Great Rus," Putin said following a meeting with Ukraine's top Orthodox clergy.
"All of us are spiritual successors of what happened here 1025 years ago. And in this sense we are certainly one people."
However, casting a shadow over the visit, feminist group Femen said three of its activists and a former Moscow-based AFP photographer had been abducted shortly before a planned protest against Putin.
Femen said the four were beaten up and bundled into a car which then left in an "unknown direction".
Earlier Saturday, the group's leader Anna Hutsol said she was hit in the face by a stranger.