David Cameron believes disruption caused by today's public sector strikes is "wrong", his official spokesman said.
Asked whether the Prime Minister felt strikes in the public sector could ever be justified, the spokesman said: "Does the Prime Minister think that people in this country - parents, commuters, users of public services - should have their routines disrupted? Of course he doesn't think it is right."
Asked for the PM's assessment of the impact of today's strikes, the spokesman responded that Cameron would say "any disruption any user of public services experiences is wrong".
A government minister has said fewer than 500,000 people are estimated to have taken part in today's public sector strike, a significantly lower number than union leaders have claimed.
Cabinet Office Minister Francis Maude, who is responsible for the Civil Service, said: "Our official estimates are that fewer than half a million took part in this strike action – well short of the inflated claims of union leaders.
"Within the Civil Service, there has been the lowest recorded turnout for a national strike," he added.
David Cameron, Michael Gove and other Government figures depicted in a variety of unflattering manners by striking public sector workers.Read the full story ›
Labour leader Ed Miliband said the industrial action taken by public sector workers today was "a sign of failure on signs".
He said: "We don't support the strikes because they are a sign of failure on all sides.
"I think the Government bares a share of responsibility for another reason too; they promised low paid workers a £250 pay rise and it didn't happen, they've demonised teachers and I'm not going to demonise public sector workers."
A union has described the Cabinet Office's figures on the amount of people striking today as "laughable".
The Cabinet Office claims a fifth of civil servants - around 90,000 people - are on strike compared with a third in the last big walkout in 2011.
However, the Public and Commercial Services union dismissed the Cabinet Office's claims, saying: "No-one can trust this government to keep reliable figures, it can't even tell us what it's done with dozens of Home Office files."
Cabinet Office Minister Francis Maude said fewer than 20% of civil servants were on strike today compared with a third in the last big walkout in 2011.
Mr Maude said today's disruption was the fault of union leaders and urged public sector workers that the right to strike must be exercised "responsibly".
He pointed out that only one in five members of Unite and Unison had taken part in ballots leading to the strike, adding that low turnouts strengthened the case for reform.
Education Secretary Michael Gove told ITV News there is "no excuse" for teachers going on strike, which has "caused disruption for hardworking parents".
Mr Gove said: "There's no justification for this action and teachers, I hope, will draw the appropriate lesson from today which is that it is their responsibility to put children first and to be in the classroom teaching, not on the picket line striking."
Public sector workers in Britain have gone on strike today in a row over pay, pensions, conditions, jobs and spending cuts.