UNITED NATIONS (Reuters) - U.N. Secretary-General Antonio Guterres spoke separately on Monday with the foreign ministers of Russia and Ukraine and still believed "from his own analysis, his own hopes" that there would not be a conflict, a U.N. spokesman said.

       The United Nations has no plans to evacuate or relocate out of Ukraine any of its more than 1,600 staff - of which 220 are foreign staff and more than 1,400 are Ukranian - U.N. spokesman Stephane Dujarric also said.

       He expressed "serious concern" during his phone calls with Russian Foreign Minister Sergei Lavrov and Ukraine's Foreign Minister Dmytro Kuleba on Monday over the heightened tensions.

       "He welcomed the ongoing diplomatic discussions to defuse those tensions and underlined, yet again, the fact that there is no alternative to diplomacy," Dujarric said.

       When asked if the outreach could signal a greater mediation role for the United Nations, Dujarric said: "The Secretary-General said his good offices are always available ... It is his his duty and responsibility as Secretary-General to be in touch with many of the parties involved in this current situation."

       Guterres had said three weeks he was convinced a Russian invasion would not happen.

       (Reporting by Michelle Nichols; Editing by Angus MacSwan)