( CNBC.com )

It’s a day of high-level meetings on Thursday, with an extraordinary NATO summit taking place in Brussels, as well as meetings of EU leaders and the G-7.

NATO is expected to commit to “major increases” in troop numbers along its eastern flank, with Secretary General Jens Stoltenberg telling CNBC ahead of the summit that Russian President Vladimir Putin had made “a big mistake.”

Additional assistance for Ukraine is also expected to be announced, as well as possible extra sanctions on Russia, when U.S. President Joe Biden meets his EU counterparts.

Meanwhile, the British government said that Ukrainian forces were carrying out successful counterattacks against Russian units on the outskirts of Kyiv and may be regaining lost ground.

The White House has set up a team of experts to plan how the United States could respond should Russia use weapons of mass destruction – chemical, biological or nuclear – during its invasion of Ukraine, senior administration officials said on Thursday.

Russia has repeatedly raised the prospect of using nuclear weapons as it struggles to overcome Ukraine’s military during the month-old war that the Russian government calls a “special operation.” This week, the Kremlin said such weapons would only be used in the case of an “existential threat.”

U.S. officials have warned that Russia’s accusations that Ukraine might use chemical weapons are a lie, and also an indication Moscow may resort to their use, given past precedent.

The White House National Security Council sent an internal memo to agencies on Feb. 28 to create a strategy group to examine major geopolitical shifts that are occurring as a result of Russia’s invasion of Ukraine, officials said. A second group, known internally as the “Tiger Team,” is looking at what the next three months look like.