Ban Ki-moon heading to Russia and Ukraine

United Nations Secretary-General Ban Ki-moon was on Wednesday preparing to set off for Russia and the Ukraine to encourage a peaceful settlement of the crisis threatening conflict between them.

Ban will meet with Russia's President Vladimir Putin in Moscow on Thursday and with Ukraine's interim leaders President Olexsandr Turchynov and Prime Minister Arseniy Yatsenyuk in Kiev on Friday.

"The Secretary-General has consistently called for a solution that is guided by the principles of the United Nations Charter," Ban's office said, urging "all parties to resolve the current crisis peacefully."

Moscow and Kiev are on the brink of conflict following a breakdown in relations in the wake of last month's overthrow of Ukraine's former Kremlin-backed president Viktor Yanukovych.

On Tuesday, Putin signed a treaty absorbing the Ukrainian region of Crimea into Russia and on Wednesday pro-Russian troops stormed a Ukrainian naval headquarters on the peninsula.

UN spokesman Farhan Haq said Ban was "calling for a de-escalation and restraint from all sides and he will continue to plead for that when he goes to Russia and Ukraine."

"(Ban) wants to build a constructive dialogue ... between Moscow and Kiev aimed at agreeing on specific measures that will pave the way to a diplomatic solution," Haq said.

"He believes that although matters have been difficult in recent days, the path towards a peaceful resolution of the crisis is still open," added Haq.

Much of the international community, including the United States and the European Union, rejects the annexation of Crimea as illegal, but Moscow in turn refuse to recognize the Ukrainian government.

US President Barack Obama has invited G7 leaders to meet in The Hague on Monday on the sidelines of the Nuclear Security Summit to discuss Ukraine.

UN diplomats have been deployed to Ukraine by Ban since the start of the crisis, with envoy Robert Serry followed by deputy Jan Eliasson and UN Human Rights chief Ivan Simonovic.

None has been able to convince Moscow or Kiev to start a dialogue. Serry was forced to leave Crimea abruptly after threats from armed men, while Simonovic aborted a trip to the disputed region for logistical and security reasons.

Thirteen of the 15 members of the UN Security Council backed a US draft resolution unequivocally condemning Crimea's referendum last weekend on joining Russia. The resolution was vetoed by Moscow while China abstained.