Russia’s top security agency says it has arrested four Russians accused of making preparations to kill senior Defense Ministry officials on Ukraine's orders.

To ensure the safety of civil aircraft flights, temporary restrictions have been introduced on the operation of Sheremetyevo, Domodedovo, Vnukovo, Zhukovsky and Kaluga airports,” Russia’s aviation authority said.

President Vladimir Putin said on Thursday there was no time left this year to sign a new Ukrainian gas transit deal, and laid the blame firmly on Ukraine for refusing to extend the agreement that brings gas to Slovakia,

"Ukraine was brutally attacked on Christmas Day," said Keith Kellogg, President-elect Donald Trump's pick for Ukraine and Russia envoy.

The missile has been branded as Ukraine's answer to dwindling Western aid, building self-reliance in defense technologies.

Iranian President Masoud Pezeshkian is set to visit Moscow on Jan. 17 and sign a cooperation agreement with Russian President Vladimir Putin, Russian state news agency RIA cited Iran's ambassador to Russia as saying on Thursday.

Vladimir Putin declared on Thursday that Russia was closer to reaching its goals in Ukraine and that the front line was advancing every day.

A Russian general who was wanted by Ukraine for using chemical munitions was killed by a remotely detonated bomb in Moscow on Tuesday, Russian authorities said.

Igor Kirillov, who was named the head of Russia’s nuclear defense forces in April 2017, was under sanctions from several countries including the U.K. and Canada for his role in Ukraine.

“While other countries of the world are celebrating Christmas, Ukrainians are continuing to suffer from endless Russian attacks,” Ukraine’s human rights ombudsman Dmytro Lubinets wrote on Telegram.

Russia's ballistic missile attack on Ukraine’s capital, Kyiv, killed at least one person; a Ukrainian attack on Russian border town killed six, officials say.