By Louis Charbonneau and Michelle Nichols UNITED NATIONS (Reuters) - The United Nations worked quickly on Monday to salvage fragile international bids to broker peace in Syria and Yemen from a spillover of tensions between Saudi Arabia and Iran after Riyadh's decision to cut off ties with Tehran. U.N. Secretary-General Ban Ki-moon on Monday told Saudi Foreign Minister Adel al-Jubeir he was extremely troubled by the break in ties, his spokesman Stephane Dujarric said.