U.S. military assistance to Ukraine now will at best be marginal in affecting the outcome of the Russia-Ukraine crisis. It might be morally justified to help a U.S. partner at risk of aggression. But given the scale of the potential threat to Ukraine and its forces, the most effective way Washington can help is to work on finding a diplomatic solution.

Russia insists that there was an agreement not to expand Nato eastwards after the end of the USSR. History begs to differ.

Sixth OSCE Summit of Heads of State or Government, Istanbul, 18-19 November 1999. Includes Charter for European Security, Istanbul Summit Declaration, Vienna Document 1999, Final Act of the Conference of the States Parties to the Treaty on Conventional Armed Forces in Europe.

The Organization for Security and Co-operation in Europe says violations were concentrated within the Donetsk region.

NATO chief Stoltenberg says alliance is also beefing up arms support to Kyiv and reinforcing defences on allied areas.

UN General Assembly demands Russia stop its offensive in Ukraine, voting 141 to five with 35 abstentions.

Ukrainian defenders of the besieged port of Mariupol will fight to the end against Russian forces, the country's prime minister says.