KYIV, Ukraine -- Russia launched a second major drone and missile bombardment of Ukraine in four days, officials said Tuesday, aiming again at the power grid and apparently snubbing U.S.-led peace efforts as the war approaches the four-year mark.

Russia on Tuesday condemned what it described as "subversive external interference" in Iran's internal politics and said U.S. threats of new military strikes against the country were "categorically unacceptable.

It is difficult to determine how many foreigners have joined Russia's military. BBC Russian's analysis - which also looked at the number of foreigners killed and injured - suggests at least 20,000 may have signed up, including from countries such as Cuba, Nepal and North Korea.

The state Investigative Committee said the suspected crimes were negligence, and causing death by negligence. It did not say who was under investigation.

A Ukrainian drone strike killed one person and wounded three others in the Russian city of Voronezh, local officials said Sunday. Meanwhile, thousands of residents were still without power in Kyiv, following an intense Russian bombardment.

Russia says it used its new Oreshnik hypersonic missile and other weapons in a massive strike on Ukraine​. Ukrainian President Zelenskyy says a drone hit the Qatar embassy.

In November, Venezuela's National Assembly approved a 15-year extension of the joint ventures between state company PDVSA and a unit of Russia's Roszarubezhneft that operate two oilfields in the South American country's western region.

Russia attacked Ukraine overnight with 242 drones and 36 missiles, the Ukrainian Air Force said Friday morning.

Moscow said the overnight strike was in response to an alleged Ukrainian drone strike on a residence used by President Vladimir Putin, which the U.S. and others said did not happen.

The hypersonic Oreshnik intermediate range ballistic missile hit Ukraine's western Lviv region late Thursday night, although officials there did not mention any casualties.

Russia and China allegedly expanding Arctic presence for military reasons, conducting joint patrols near Alaska and Canada, top NATO commander warns.