Ukraine and Russia: What you need to know right now

(Reuters) - U.S. President Joe Biden said he doubted whether Russian President Vladimir Putin would use a tactical nuclear weapon as Ukraine pleaded for a rapid increase in western military aid to defend against missile strikes on its cities.

DIPLOMACY

* More than 50 countries will gather on the sidelines of a NATO meeting in Brussels to discuss bolstering Ukraine's air defence, two days after Russian missiles rained down on cities across the country, including the capital Kyiv.

* NATO told Moscow it would meet any attacks on allies' critical infrastructure with a "united and determined response" and was monitoring Russia's nuclear forces closely as the country was "losing on the battlefield" in Ukraine.

* The Group of Seven (G7) nations committed to support Ukraine for as long as it takes, adding in a statement after a leaders' call that any use by Russia of nuclear weapons would bring severe consequences.

* Russian Foreign Minister Sergei Lavrov said Moscow will not turn down a meeting between Putin and Biden at a forthcoming G20 meeting and would consider the proposal if it receives one.

CONFLICT

* Russia's Federal Security Service (FSB) said that it had detained five Russians and three citizens of Ukraine and Armenia over the explosion that damaged the Crimea Bridge last Saturday.

* Russia hit about 30% of Ukraine's energy infrastructure in its missile attacks on Monday and Tuesday, Ukraine's Energy Minister Herman Halushchenko told CNN in an interview.

* Prosecutors for International Mobile Justice teams are investigating as possible war crimes the ongoing Russian missile strikes in Kyiv and cities across Ukraine that have so far killed at least 26 people, an official told Reuters.

ECONOMY

* Polish pipeline operator PERN said on Wednesday that it detected leak in one line of the Druzba oil pipeline on Tuesday evening. PERN said at this point the causes of the leak in the pipeline are unknown.

* Already blighted by Western sanctions, Russia's economy now faces a more self-inflicted blow, with Putin's military mobilisation drive threatening to undermine productivity, demand and recovery.

* The current energy shock, especially in Europe, is not transitory, and the geopolitical realignment of energy supplies occurring in the wake of Russia's war in Europe is both "broad and permanent", the IMF said.

QUOTES

* "(Putin) thinks that if he scares the population, he can ask for concessions, but he is not scaring us. He is pissing us off," said Viktoriya Moshkivski, 35, as she, her husband and their two sons waited for the air raid all-clear in Kyiv's Zoloti Vorota underground station.

* "We warn and hope that they realise the danger of uncontrolled escalation in Washington and other Western capitals," Russian Deputy Foreign Minister Sergei Ryabkov was quoted as saying by RIA news agency.

(Compiled by Simon Cameron-Moore; Editing by Michael Perry and Alex Richardson)