Ukrainian President Volodymyr Zelensky said on Monday evening that intelligence suggests Russia is preparing another major attack on Ukraine.

Zelensky said the attack, which could happen in the next few days, could include drones which might take out air defences and missiles, urging Ukrainians to pay attention to air raid sirens.

Russia wants to take advantage of the cold weather, Zelensky surmised. In many regions of Ukraine, temperatures are currently falling to double digits below zero degrees Celsius at night.

On Thursday, Zelensky warned of a major night-time attack by Russian forces. Hours later, Russia's military launched a fierce attack on the western Ukrainian region of Lviv, which it said included the use of its new Oreshnik medium-range missile.

In the capital, Kiev, the attack caused such severe power, water and heating outages that Mayor Vitali Klitschko advised residents to temporarily leave the city.

Russia has been waging a destructive war against Ukraine for almost four years.

Zelensky sees progress in talks with US representatives

In his evening video address, Zelensky also spoke of progress in the exchange between the Ukrainian negotiating team and US representatives.

He said most of the documents were ready to be signed, without providing further details. Zelensky said he expected the Davos format to be very successful in terms of relations with Ukraine's partners and its reconstruction after the Russian attacks.

The World Economic Forum traditionally takes place in the Swiss resort of Davos at the beginning of the year. It is actually the annual meeting of its members, predominantly large companies, which are meant to use the forum to consider how they can contribute to solving global crises.

Politicians have been using the forum for informal discussions for many years.