KIEV (Reuters) - Ukraine's parliament approved Arseny Yatseniuk for a new term as prime minister on Thursday in a ceremony that countered reports of high-level disunity in a message to Russia over its backing of separatists in the country's east.

Pomp and emotion characterized the opening of Ukraine's first parliament since the February fall of pro-Moscow president Viktor Yanukovich as his successor, Petro Poronshenko, declared in a keynote speech that there could be no future formula for Ukraine other than that of a single, unified state.

More than two thirds of the deputies in the 450-seat parliament voted for Yatseniuk to stay as head of government, a post he has held since protests toppled Yanukovich, prompting Russia to annex Ukraine's Crimea region and back pro-Russian rebels in the east.

In a gesture aimed at deflecting impressions of damaging rivalry between him and Poroshenko which have also alarmed Western governments, Yatseniuk raised his hand to the president and declared to cheers: "Here is my hand for carrying out all that you have just said from this tribune.

"This is our joint responsibility," he added before striding over to Poroshenko and warmly embracing the president.

The display of unity was scripted in part for the eyes of Russia, which is backing Russian-speaking separatists in Ukraine's industrial heartland in a conflagration that has killed more than 4,300 people.

Political parties in favor of closer links to the European Union scored a resounding victory in a Oct. 26 election, handing Poroshenko a mandate to end the conflict and steer the ex-Soviet republic further out of Russia's orbit toward Europe.

But there have been reports of disputes between Poroshenko and Yatseniuk over the share-out of portfolios in the new government which may emerge next Tuesday.

Poroshenko said 100 percent of Ukrainians favored a unitary state without federalization, a political model that has been pushed by Russia but is seen by Kiev as a recipe for the country's dismemberment.

"These are our warm wishes to those in the East or West who advise federalization," Poroshenko said sarcastically.

But he said the reality was that Ukraine would always have "to sleep with a revolver under the pillow", an allusion to the perceived threat from Russia, which in turn sees Kiev's tilt toward the EU and NATO fold as menacing.

Poroshenko said support among Ukrainians for joining NATO had grown 3-4 fold this year and Ukraine's current non-aligned status no longer worked.