Boris Johnson says he will seek to reduce unskilled migration coming into the UK, if the Tories win the election.
Home Secretary Priti Patel made a commitment on Wednesday to reduce "overall" immigration to the UK.
Asked about it, she said the Tories would "look to reduce the numbers" through better immigration controls but would not set "arbitrary" targets.
Mr Johnson was also asked whether immigration would go down under a future Tory government.
The prime minister said: "I certainly think that when it comes to people who don't have a job to go to and are coming in in an uncontrolled way, we certainly need to be reducing that."
But he he added that he was "in favour of people of talent coming to this country".
Mr Johnson claimed in the past 20 years, the UK had seen "a lot of people coming without a job to go to", who were "putting pressure on public services" and did not "necessarily have the skills that the economy demands".
Both Mr Johnson and Mrs Patel reiterated the Conservatives' plan for a "points-based" immigration system, which would apply to EU and non-EU migrants.
Labour has yet to announce its policy on immigration.
But Jeremy Corbyn said he would commit to "a fair immigration process that recognised the huge contribution made by migrant workers to this country".
"We have got to be realistic about the needs of our economy for bringing workers in, skilled workers in to help us," he added.
An SNP spokesman said cutting immigration would be "hugely damaging" for the Scottish economy and called the issue to be devolved to the Scottish government.
And the Lib Dems' home affairs spokesperson Christine Jardine called the Conservatives' approach "an insult to the millions who have come to the UK and made it their home".
Ms Patel said in a statement released by the party on Wednesday: "We will reduce immigration overall while being more open and flexible to the highly skilled people we need, such as scientists and doctors.
"This can only happen if people vote for a Conservative majority government so we can leave the EU with a deal."
However, in an interview on Thursday, Ms Patel stopped short of committing to reducing the overall numbers of people coming to the UK.
She said her party's policy would be "firm but fair while at the same time we can absolutely look to reduce the numbers in the system by having control over our immigration policy".
Asked if the Conservatives would set a target for reducing immigration, Ms Patel said targets were "arbitrary" adding "clearly that is where public confidence has been eroded in the past".
The Conservatives had previously pledged to cut net migration - the difference between the number of people entering and leaving the country - to below 100,000.
Security Minister Brandon Lewis acknowledged that, by not fulfilling the pledge, the Conservatives had "let people down".
Ms Patel said a future Conservative government would seek to control immigration numbers through a points-based system.
Under a points-based system, immigration applicants are assigned points according to a number of professional and personal characteristics, with higher points awarded for certain traits such as proficiency in the English language.
The Conservatives say they will end free movement from the EU on 1 January 2021, if they win the election and get their Brexit deal through by 31 January.
The government's immigration strategy fell into the parliamentary dustbin when the election was called.
We still await the party manifestos but today the home secretary said in a press release: "We will reduce immigration overall."
Asked to repeat this for the TV cameras later in the afternoon, she repeatedly refused, speaking only about "controlling" immigration.
The reason this is difficult territory for the Conservatives is that in some part of the UK, migrant workers are desperately needed to keep public services going.
The prime minister is known to favour a policy that works for the needs of the economy, even if that means migration numbers remain broadly where they are.
Immigration is not the electoral issue it once was - pollsters say it is at its lowest level of concern for almost two decades.
But some communities remain concerned that foreign arrivals put extra pressure on public services and jobs and those voters are often in the Labour seats that the Tories are looking to take.
'Heed public concerns'
Labour members backed a party conference motion in September defending the right of EU migrants to live and work in the UK, to reject any immigration system based on quotas, caps, targets or incomes, and to extend migrant rights.
But there is a debate at the top of the party over whether to include such a commitment in the party's general election manifesto, which is set to be finalised at a weekend meeting of its national executive committee.
Unite union leader Len McCluskey, a key ally of Jeremy Corbyn, said extending free movement would not be "sensible", telling the Guardian that the only beneficiaries of uncontrolled immigration were "the bosses of unscrupulous companies".
"It's wrong in my view to have any greater free movement of labour unless you get stricter labour market regulation," he said.
He said Labour had to heed public concerns over levels of unskilled immigration, as it was used to undercut the pay and conditions of British workers.
"If you don't understand those concerns, you fail to grasp the divisions that exist," he said.
"If we don't deal with the issues and concerns, we will create a vacuum that will be filled by a far right seeking to become the voice of the white working class."
Meanwhile, shadow home secretary Diane Abbott said a Labour government would "extend freedom of movement rights to all those legally entitled to be here".
Labour promised to end free movement from Europe - which is a condition of EU membership - in its 2017 general election manifesto, but some of the party's senior figures want to remain in the EU.
Labour have said, if they win power, they will tear up Boris Johnson's Brexit agreement with the EU and negotiate a better deal based on a much stronger relationship with the EU's single market.
Some within the party see Norway, which is outside the EU's political institutions but remains part of the single market as a member of the European Economic Area (EEA), as a model for the UK's future relationship.
But the Conservatives claimed that if the UK was to remain in the EEA, it would have to accept free movement rules and that would see levels of net migration to the UK of 260,000 each year over the next decade
If free movement rights were extended to non-EU countries, the Conservatives estimated that this figure could rise to an average of 840,000 a year - a number it said was based on "official figures and the government's own methodology".
This is based on the assumption that Labour would allow free movement with the rest of the world and that the economy would continue to grow at its current level.
According to the latest official figures, net migration totalled 226,000 in the year to March 2019.
Although numbers have remained "broadly stable" since the end of 2016, EU immigration to the UK is currently at its lowest level since 2013.
Labour said the Tories were knowingly misleading the public on its conference motion, which has no mention of geographically extending freedom of movement to other countries.
Asked whether maintaining and extending free movement from the EU would be in their manifesto, Mr Corbyn said what goes in the manifesto is "not necessarily every last dot and comma of every resolution passed at conference".
On Conservative accusations that immigration would rise under Labour, he said: "I've no idea where they get those figures from - I suspect they just, quite simply, make them up."
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