Tensions are rising after the visit of two top US officials to Kiev late on Sunday, with Russia unleashing a string of attacks Monday against rail and fuel installations deep inside Ukraine, and far from the front lines. Meanwhile, Russia’s top diplomat warned against provoking World War III, with the West offering more military assistance to Ukraine, and said the threat of a nuclear conflict “should not be underestimated.” United Nations Secretary-General Antonio Guterres pleaded on Tuesday for a ceasefire in Ukraine "as soon as possible," during his first trip to Moscow since the start of the Russian offensive. "What interests us a lot is to find the means to create the conditions for an effective dialogue, to create the conditions for a ceasefire as soon as possible," said Guterres ahead of talks with Russia"s Foreign Minister Sergei Lavrov. It is possible to have a "serious dialogue on how to best work to minimize the suffering of people", he said, adding that the situation in Ukraine is "complex, with different interpretations of what is happening there." Lavrov said the pair would discuss “the situation around Ukraine that acts as a catalyst for a great number of problems which had piled up over recent decades in the Euro-Atlantic region.” Guterres will be received by Russian President Vladimir Putin, after his meeting with Lavrov. Meanwhile, US Defense Secretary Lloyd Austin has pledged that Ukraine’s allies will “keep moving heaven and earth” to help Kyiv defend itself against Russia. He made the comment at a NATO-EU meeting on Tuesday between more than 40 countries in Germany on arming Ukraine. “This gathering reflects the galvanized world," said Austin. Since Russia’s invasion in February, more than 30 allies and partners joining the US in sending military aid to Ukraine, committing around $5 billion worth of equipment. Addressing Ukraine, he added: “We know, and you should know, that all of us have your back and that’s why we’re here today — to strengthen the arsenal of Ukrainian democracy.” Also, a sixth package of European Union sanctions against Russia in response to its invasion of Ukraine is expected "very soon", the bloc"s energy policy chief said on Tuesday. The exact date of the package is not yet confirmed, and as with the previous rounds of EU sanctions it would need approval from EU countries, EU energy commissioner Kadri Simson told a news conference in Warsaw. Germany, in another development, said it will authorize the delivery to Ukraine of "Cheetah" type tanks, a government source announced on Tuesday, according to AFP, which would constitute a major turning point in the so far cautious approach Berlin has taken to sending military supplies to Ukraine. The details and number of tanks, which are specialized in anti-aircraft defense, will be revealed during the meeting of representatives from more than 40 countries being held today in Germany, the news agency reports. Meanwhile, AP reports that Germany has cleared the delivery of Gepard anti-aircraft guns to Ukraine. This is according to the text of remarks given by German Defense Minister Christine Lambrecht at a US-hosted meeting being held Tuesday at the United States’ Ramstein Air Base in Germany. Turkish President Recep Tayyip Erdogan has urged Russian President Putin to agree to direct talks with his Ukrainian counterpart. The call comes in the wake of Turkish diplomatic efforts to defuse the crisis over Russia"s war in Ukraine, including by hosting Ukrainian and Russian negotiators for talks in Istanbul late last month. The Turkish presidency said in a statement Tuesday that Erdogan proposed taking the “Istanbul process to the level of leaders, a crucial threshold in the Russia-Ukraine negotiations.” It sought to continue the “positive progress of the Istanbul talks” toward peace. Talks stalled after Ukrainian President Volodymyr Zelenskyy accused Russian troops of committing war crimes. Putin later said peace efforts were at a dead end. Ankara, which maintains close ties to both Kiev and Moscow, has presented itself as a neutral broker in a bid to end the fighting. The United Nations on Tuesday doubled its emergency appeal for humanitarian aid to Ukraine. “More than $2.25 billion is now required to meet the needs in Ukraine, more than double the amount requested ($1.1 billion) when we launched the appeal on March 1, days after the start of the war. The appeal has also been extended from three to six months," the agency said. Meanwhile, the UN said it now expects Ukrainian refugees numbers to reach 8.3 million, up from around 5 million today. Ukrainian MP Lesia Vasylenko has made it clear what she hopes to see as a result of today"s meeting of over 40 defense ministers being held in Germany: "Weapons, weapons, weapons!" — Euronews