Ukraine's acting defense minister, Ihor Tenyukh, says Russia has agreed on a truce in Crimea until March 21.
Speaking in Kyiv, Tenyukh said the truce was reached with Russia's Defense Ministry and Russia's Black Sea Fleet on March 16.
The announcement came as voters in Crimea cast ballots in a local referendum asking whether the peninsula should break away from Ukraine and become part of Russia.
Russian soldiers have been blocking Ukrainian armed forces inside their bases in Crimea since the Kremlin deployed troops across the peninsula on February 28.
Warships from Russia's Black Sea Fleet -- which is based at the Crimean port of Sevastopol under a long-standing agreement with Ukraine -- also have been facing off against Ukrainian naval vessels in a tense standoff.
Tenyukh said that under a five-day-truce, Russia has promised that "no measures will be taken against our military facilities in Crimea" until March 21.
He said Ukrainian military facilities on the peninsula are "therefore proceeding with a replenishment of reserves."
Meanwhile, Ukrainian forces on the mainland remained on high alert on March 16 -- one day after the Defense Ministry in Kyiv said Russian forces had tried for the first time during the crisis to enter Ukrainian territory north of Crimea.
Ukrainian border guard spokesman Oleh Sobodan said about 120 Russian soldiers on March 15 took control of a natural-gas distribution station near the village of Strilkove in Ukraine's Kherson Oblast, about 10 kilometers north of the administrative border with Crimea.
The head of Strilkove's village council, Oleksandr Ponomarev, told journalists later that a Russian assault force initially had landed on the outskirts of the village by mistake before advancing to the gas-pumping stations.
Ponomarev also said the Russian troops told him their operation was aimed at "ensuring the protection of the gas-pumping station" and the Sea of Azov wells in the Strilkovoye gas field that are operated by Chornomornaftogaz.
Chornomornaftogaz is headquartered in the Crimean capital, Simferopol. But it is a subsidiary of Ukraine's Kyiv-based, state-owned Naftohaz -- which is subordinated to the Ministry of Fuel and energy in Kyiv and currently is responsible for transferring gas to Russia's Gazprom.
The March 16 truce announcement made no mention of tensions along Ukraine's northern and eastern borders with Russia, where thousands of Russian troops -- backed by armor, multiple-rocket launchers, heavy artillery, and helicopter gunships -- have been deployed during the past week.
The Kremlin has said those deployments within Russian territory near Ukraine's border are part of a military training operation.
In Kyiv on March 16, Ukrainian Prime Minister Arseniy Yatsenyuk called for foreign observers from the Organization for Security and Cooperation in Europe (OSCE) to be urgently sent to Ukraine's eastern and southern regions.
In a statement, Yatsenyuk said the OSCE's mandate "should include the east and south of Ukraine, including Crimea."
The Kremlin said the same day that Russian President Vladimir Putin, in a telephone call with German Chancellor Angela Merkel, expressed concern about tensions he says are being caused by radical groups in Russian-speaking regions of Ukraine's south and southeast.
Thousands of pro-Russian demonstrators protested in major eastern Ukrainian cities on March 16 including Kharkiv and in Donetsk, where the mob broke through a police line and stormed the prosecutor's office, eventually raising a Russian flag from an upper floor of the building. The Donetsk protesters were demanding the release of detained separatist leader Pavel Gubarev (see video below).
Based on reporting by Reuters, AFP, RFE/RL, Ukrainian News Agency, and ITAR-TASS and Interfax