LONDON, Dec. 7 (Xinhua) -- British Prime Minister Boris Johnson and European Commission President Ursula von der Leyen are expected to make a telephone call at 16:00 (1600 GMT) on Monday to unlock the stalemate in post-Brexit trade talks, local media reported.

The BBC said the the scheduled phone call is "crucial" as the time is running out before the Dec. 31 deadline is around the corner.

In their upcoming phone conversation, the second one in 48 hours, the two leaders will "assess whether a post-Brexit trade agreement can still be reached," Sky News reported.

Wednesday is seen by both London and Brussels as the final day a Brexit deal could be done, reports quoted European Union (EU) sources as saying.

The two leaders had their first phone conversation on Saturday after both sides' chief negotiators paused their talks over major differences on three core issues, namely level playing field, governance and fisheries.

After the hour-long call, during which Johnson and von der Leyen agreed on a final push to get an agreement, negotiators from Britain and the EU resumed their talks in Brussels on Sunday to secure a trade deal before the Brexit transition period expires at the end of this month.

The British and EU leaders issued a joint statement after a phone call on Saturday afternoon, saying that the trade talks will reconvene in Brussels on Sunday, even though "significant differences remain."

The British and EU chief negotiators wrote on Twitter on Friday that "the conditions for an agreement are not met, due to significant divergences on level playing field, governance and fisheries."

The two leaders had phone conversations several times instead of face-to-face discussions due to the COVID-19 pandemic.

To bring life back to normal, countries including Germany, China, Russia, and the United States are racing against time to find a vaccine.

The second phone call comes as the British and EU negotiators are meeting in Brussels for the post-Brexit talks, which are on a "knife edge" as their major differences on the three sticking points still remain.

Also on Monday, Britain said that it is prepared to negotiate a deal for Brexit for as long as it takes, but it also rejected any extension of a Brexit transition period or further talks past this year.

A spokesman for the prime minister said, "We are prepared to negotiate for as long as we have time available, if we think an agreement is still possible."

On the possibility of talks continuing next year, the spokesman said, "I can rule that out."

The pound fell sharply on Monday morning after the EU's top negotiator Michel Barnier issued a "very downbeat" assessment of the chances of a Brexit deal.

His gloom-laden private breakfast briefing to EU ambassadors in Brussels seemed calculated to stoke fears of a no-deal outcome, and sterling dipped by 1.15 percent against the euro within minutes.

An EU diplomat said, "We are at the make-it-or-break-it moment."

Britain and the EU started their lengthy and bumpy post-Brexit talks in March after Britain ended its EU membership on Jan. 31, 2020, trying to secure a future trade deal before the Brexit transition period expires.

The negotiations are at a crucial stage as time is running out for both sides to secure a deal before the Brexit transition period expires at the end of the year. Failure to reach a free trade agreement with the EU means bilateral trade will fall back on World Trade Organization (WTO) rules in 2021.