NATO Secretary General Jens Stoltenberg has said the military alliance is ready to support Ukraine for years to come in the war against Russia, the media reported.
Speaking at a youth summit in Brussels, Stoltenberg said, "We need to be prepared for the long term," BBC reported.
He added that "there is absolutely the possibility that this war will drag on and last for months and years", the report said.
NATO countries -- alongside nations that are not part of the alliance -- met in Ramstein, Germany, earlier this week to discuss how they can support Ukraine's defence and security.
The Nato chief said Ukraine's allies are preparing to provide it with NATO-standard weapons.
Several countries have been sending military assistance and financial aid to Ukraine since Russia's invasion on February 24.
The Kremlin has warned the West that sending heavy weapons to Ukraine threatens security on the European continent, BBC reported.
Russia's Foreign Ministry singled out the UK for criticism, saying it was encouraging Ukraine to attack Russia within the Russian territory.
"Further provocation prompting Ukraine to strike against Russian facilities will be met with a harsh response from Russia," a spokesperson said.
Russia would not allow Western officials visiting Ukraine to deter it from launching retaliatory strikes on nearby Ukrainian targets, the spokesperson warned, adding: "Advisers from Western countries staying in Ukraine's decision-making centres will not necessarily be a problem for Russia's response measures."