Theresa May has indicated that the Conservatives will again promise to cut net migration to the "tens of thousands" in their election manifesto.
Speaking in Harrow, she said migration levels were having an impact on public services and low-paid workers.
Asked if this meant the target - missed repeatedly since 2010 - could be hit, she said it was important to continue to aim for "sustainable" levels.
Other parties said the target was "artificial" and should be dropped.
On Sunday, Home Secretary Amber Rudd refused to say whether the pledge - which was in the 2010 and 2015 Tory manifestos - would be repeated but the BBC understands it will definitely be in the 2017 manifesto, due to be published next week.
Net migration is the difference between the numbers of people moving to the UK for more than a year, and the numbers of people leaving the UK to live elsewhere for a year or more. The most recent figure was 273,000 and the last year that it was below 100,000 was 1997.
Questions had been raised about whether the target would be retained after Culture Secretary Karen Bradley recently said that immigration was "not about putting numbers on it" but about ensuring Britain had the skilled workers it needed.
By political editor Laura Kuenssberg
While Theresa May has recommitted to the target that she, as home secretary, missed for six years in a row, ministers have been busy reassuring businesses they will be able to get the people they need, whether builders, bankers, or fruit pickers. If the economy needs them, they will be allowed to come.
That doesn't sound like a recipe for getting the numbers down to Theresa May's preferred level. And even though we are on our way out of the EU, there is still huge scepticism over whether the target is remotely achievable. So why keep it?
Ms Rudd told BBC Radio 5 live's Pienaar's Politics on Sunday that while she believed immigration should be lower, the party had a "lot to think through" and the manifesto would not be "identical" to previous ones.
But on a campaign visit in north-west London, Mrs May indicated there would be no back-tracking from the target. Net migration numbers, she said, had gone up and down over the past few years but the commitment still stood.
"I think that it is important that we do say and continue to say that we do want to bring migration to sustainable levels. We believe that is the tens of thousands."
She added: "Once we leave the EU, we will of course have the opportunity to ensure we have control of our borders. We will be able to establish our rules for people coming from the EU. That is a part of the picture we have not been able to control before."
EU migrants accounted for about 44% of the 596,000 people who came to the UK in the year to last September,
Of these, an estimated 294,000 came to work, 134,000 were long-term students, 74,000 came to join existing family members while 61,000 came for other reasons - including asylum seekers and those receiving medical treatment.
Before the Brexit vote, the Conservatives sought to reduce the "pull factors" which it said were attracting EU migrants, such as access to benefits. Now they have promised new migration controls once freedom of movement no longer applies, but they have yet to set out the precise model they would adopt.
Dr Carlos Vargas-Silva, from Oxford University's Migration Observatory, said he expected the target to apply to a longer period than five years and possibly exclude certain groups.
"The key question is to what point this is going to be a flexible target... and react to the economy and new developments in the country," he told BBC Radio 4's Today.
"The previous one was fixed. It did not change over five years. Maybe this one will be adjusted along the way."
But he said ministers would still face the challenge of reducing levels of migration from outside the EU. Although figures are currently at a three year low and well down on 2010, they remain above the 250,000 mark. Students currently account for about 70% of the total.
Labour says it accepts that the principle of the free movement of people - which EU leaders say goes hand-in-hand with single market membership - would have to end after Brexit but that new immigration controls should not be the "overarching priority" as the UK leaves.
Jeremy Corbyn said migrants working in the UK's public services made a "massive contribution" and changes to the system resulting from Brexit had to be fair.
"Theresa May made that promise in 2010 and made the same promise in 2015, and didn't get anywhere near it on any occasion at all," he said.
Lib Dem leader Tim Farron said the target was a product of political manoeuvring and "meant very little" while Green Party co-leader Jonathan Bartley said it had helped "split up families and encouraged hostility towards migrants".
UKIP said the target was "vacuous" and the Conservatives had broken their promises "time and time again" on the issue.
Announcing its own proposals, including a five-year ban on unskilled and low-skilled foreign labour, it said its ambition to reduce net migration to zero would put "clear water" between itself and the other parties.