A gloomy mood has descended over Kyiv. Just over 200 miles away, 100,000 Russian soldiers are gathering on the border. Ukrainians are preparing for an invasion.

Today, senior US officials will meet with their European allies. They fear that Russia could attack Ukraine at "any point". 

NATO is a group of Western countries that promise to defend each other against threats. Vladimir Putin wants to make sure that Ukraine never joins it. But NATO has refused his demand. 

Last week, peace talks failed. Some Western officials think Russia is looking for an excuse to invade Ukraine. They believe Russian president Vladimir Putin wants to expand his territory. 

Russia denies this, but many are scared that war could break out. Years of conflict in Ukraine have already killed 14,000 people.

War in Ukraine would not just affect those nearby. It could affect the whole of Europe. Many people could die. Millions more could become refugees.

Western leaders still hope to avoid war. And many think Putin will not risk it. Strict sanctions from the West could persuade him not to invade. And Ukraine's military is stronger than ever. If lots of Russian soldiers die, it could make Putin unpopular in Russia. 

Meanwhile, a war might push Ukraine and the West closer together, rather than further apart. 

Some think the costs of war could stop Putin. Others think he is determined to act. But it is clear that a war in Europe could have terrible consequences for Ukraine, Europe and the entire world. 

Yes: There is still hope. Peace talks and sanctions could persuade Putin that the risks of war are too great to continue. An invasion is not inevitable. 

No: Nothing will stop Putin from pursuing his goal of invading Ukraine. Last minute talks are doomed to fail. 

Or... No one can say for sure what Putin's intentions are. The build-up of troops may not be a warning about war. They might just be an attempt to bully Ukraine.