US Treasury Secretary Janet Yellen warned on Wednesday that sanctions on Russia over the war in Ukraine could send oil prices around the world soaring, which would penalize the US and its allies.

According to Reuters, and quoted by the Noticias ao Minuto, Yellen said she expects that US oil companies (and others) may increase production in the next six months, attracted by higher prices, which may allow stronger restrictions on Russian oil.

The European Commission on Tuesday proposed a European Union (EU) import ban on Russian coal, which is worth Russia four billion euros a year, and the expulsion of four Russian banks from the European financial market.

At stake is a new package of sanctions proposed by the EU executive and announced to the press in Brussels by the institution's leader, Ursula von der Leyen, aiming to make these restrictive measures "broader and tougher" on the Russian economy, particularly after the alleged executions of civilians committed by Russian troops.

"The four sanctions packages [previously adopted by the EU] have hit hard and limited the Kremlin's political and economic options. We are seeing tangible results, but clearly, in view of events, we need to increase our pressure even further and therefore propose to take our sanctions a step further," she explained.

According to Ursula von der Leyen, the new sanctions - which will have to be endorsed by member states - include "a ban on coal imports from Russia, worth four billion euros a year," in order to "cut off another important source of revenue for Russia."