Moscow/Berlin, 14 March 2022 (dpa/MIA) — Nineteen days into the Russian invasion of Ukraine and as fighting continues to rage across the country, a fourth round of peace negotiations between the sides was put on hold until Tuesday. The meeting via video link started on Monday afternoon but the delegations were taking a break to sort out technicalities, according to Ukrainian presidential advisor Mykhailo Podolyak. He said, however, that discussions among working groups were still under way. "Negotiations are ongoing," Podolyak tweeted. The new round of talks were to focus on "peace, a ceasefire, immediate withdrawal of all troops and security guarantees," Podolyak wrote on Twitter. In-person talks were held previously in Belarus, but there has been no breakthrough so far. The warring countries' foreign ministers also met in Turkey last week. Both Kyiv and Moscow have expressed cautious optimism about the course of peace talks, even as Russia's assault on Ukraine intensifies. In the embattled south-eastern city of Mariupol, a pregnant woman and her unborn child have died after an attack on an obstetrics ward, the Ukrainian Foreign Ministry said. A photo showing several men carrying the pregnant woman on a stretcher through the destroyed hospital complex caused a worldwide stir. However, after several failed attempts, a large number of civilians have managed to get out of Mariupol using a humanitarian corridor. The humanitarian situation in the city, which has been besieged for days, has deteriorated dramatically, and for the first time in more than a week, such a corridor has been employed successfully and not disrupted by attacks. More than 160 private vehicles left the city, heading west to the city of Berdiansk, more than 70 kilometers away, according to Mariupol city officials on Telegram. Additionally, an aid convoy with supplies for those still in the city is on its way in. Ten humanitarian corridors were planned on Monday to evacuate civilians from embattled towns and villages in Ukraine, the government in Kyiv said. According to Ukrainian Deputy Prime Minister Iryna Vereshchuk, six corridors were planned in the region around the capital Kyiv, and three more in the Luhansk region in eastern Ukraine. A bomb attack on a pumping station in the northern city of Chernihiv left the city of 300,000 people without water, according to the operator. Photos showed damage to an underground reservoir. In Kyiv, at least two people were killed in a high-rise building when an artillery shell hit while an aircraft factory belonging to manufacturer Antonov was shelled. The Ukrainian Foreign Ministry renewed calls for a no-fly zone over Ukraine, a step NATO has refused to take so far, as it would risk a direct confrontation with Moscow. Ukrainian sources have also reported that Russian troops exploded parts of an ammunition depot not far from the occupied Zaporizhzhia nuclear power plant. The blast occurred near the ruins of a military training facility, the Ukrainian nuclear power operator Energoatom said on Telegram. The information could not be independently verified. Meanwhile, in the eastern city of Donetsk, at least 20 people have been killed and nine injured by fragments of a Ukrainian missile, according to pro-Russian separatists in the region. Local separatist leader Denis Pushilin said children were among the victims. Russian President Vladimir Putin recognized the Donetsk and Luhansk regions as independent, paving the way for him to start the invasion of Ukraine. According to the UN High Commissioner for Human Rights on Monday, 636 civilian deaths have been confirmed in the war so far, including 46 children, but that the actual toll was sure to be far higher. The Ukrainian army early on Monday said that Russian troops were trying to gain a foothold in occupied positions and preparing for fresh attacks. "The enemy is forming and moving strategic reserves to our borders," the Ukrainian general staff said in a daily bulletin, adding that fresh attacks were expected on Kharkiv, Sumy and the Kyiv suburb of Brovary. In a signal that the Russian onslaught could escalate further, Kremlin spokesman Dmitry Peskov said the Russian Defense Ministry was now "not ruling out the possibility of taking full control of large populated areas that are now practically surrounded." He noted that this was a change in approach from Putin's earlier order to "refrain from an immediate attack on major population centres, including Kyiv." The chair of the Organization for Security and Co-operation in Europe (OSCE), Zbigniew Rau, said the war in Ukraine endangers the existence of the organization. He told the UN Security Council on Monday that it is questionable how effective the OSCE can be when one of its members sees violence as a way of extending its power. Impartiality ends where blatant violent violations of international humanitarian law starts, Rau said in response to accusations of partiality.