Number 10 has defended has secrecy surrounding phone calls between Boris Johnson, Emmanuel Macron and Angela Merkel over the escalating vaccines row.
European sources revealed the calls took place on Sunday - but were not disclosed by Downing Street.
The calls came amid rising tensions between the UK and EU over vaccine supplies.
European Commission President Ursula von der Leyen had said vaccine maker AstraZeneca could face a ban on exports of doses if it did not meet its delivery obligations to the bloc.
EU leaders are expected to discuss the issue at a summit on Thursday.
Phone calls between the Prime Minister and other foreign leaders are usually a matter of public record.
Under normal circumstances, No10 releases basic 'readouts' of the PM's calls with overseas counterparts.
And officials and diplomats are normally dialled in to the calls.
But asked about the PM's calls with EU leaders during a briefing on Tuesday, the Prime Minister's spokesman said: "I don't have anything to set out today in terms of calls."
It's understood Number 10 did not disclose the phone calls because were considered to be "private."
And the PM's spokesman refused to say whether officials were also on the calls.
Challenged over the secrecy today, the spokesman said: "The PM regularly speaks to the EU and European leaders as he did last week and over the weekend.
"We set out last week, we said that he spoke to Ursula von der Leyen and we set out our position that he reiterated the importance of not placing import restrictions on vaccines."
Asked why the calls were kept secret, and whether there were officials involved in the calls, the Spokesman said: "I'm obviously not going to go into details on specific calls, but as I say the PM regularly speaks to European leaders, his counterparts and as I say we've set out our position on this issue."
Allegra Stratton, the Prime Minister's press secretary indicated Mr Johnson's future calls would only be disclosed if "a decision is taken" to do so - rather than as a matter of routine.
She said: "We do give you readouts on a very regular basis.
"We will continue to do that as and when the decision is taken to give you those readouts."
A French official confirmed the call between Mr Johnson and Mr Macron - saying there was no advisor present on the French side.
The official said the call was placed at Mr Johnson's request.
