The first Syrian refugees to be taken in under the government's expanded resettlement scheme will arrive in Britain "in the coming days", Home Secretary Theresa May has said.
The UK has pledged to take up to 20,000 refugees over the next five years.
Labour's Andy Burnham welcomed the move, but questioned whether more refugees should be accepted by the UK.
Earlier, it was announced that Royal Navy ship HMS Richmond will be deployed to help tackle people smugglers.
The warship will be deployed for two months to board and seize vessels off the coast of Libya.
The government has said it will take refugees from UN camps on the border with Syria.
But the UK will not take part in a proposed EU-wide resettlement scheme for refugees who have already arrived in Europe.
In a Commons statement, Mrs May said many refugees had been through "heart shattering" experiences and seen loved ones die.
She told MPs: "I know that honourable members and the general public are keen to know more detail on the numbers and when people are expected to arrive.
"But I must underline that the scale of the expansion needs careful and meticulous planning to ensure we get it right."
The government was "working at speed" to plan for even more arrivals in the coming weeks, she said.
In response to questioning from MPs, she added that refugees would be subject to security checks to make sure Islamic State militants were not among them.
She did not say how many refugees would arrive in the first wave, but the BBC's Daniel Sandford said he understood the government was aiming to take about 400 people a month.
The UN was able to send people quickly, but security checks by the UK authorities would take time, he added.
Shadow home secretary Mr Burnham said with winter approaching and temperatures dropping, there needed to be an "urgent solution" to stop more refugees risking dangerous voyages by boat to Europe.
He welcomed last week's announcement the UK would accept 20,000 further refugees, but stressed there needed to be "clarity on headline figures".
He also queried whether the government's decision not to take any refugees from Europe was sustainable "from a moral and a practical point of view".
The SNP's Joanna Cherry QC said her party believes "the UK Government is not doing enough in the face of the extraordinary humanitarian crisis".
The home secretary said she would update Parliament on the numbers in due course.
Europe has been struggling to deal with a huge influx of refugees.
Most are fleeing the conflict in Syria but large numbers are also escaping from violence and poverty in Afghanistan, Eritrea and Kosovo.
In the latest developments, Croatia says it will allow migrants to travel on to northern Europe - opening up a new route a day after Hungary sealed its border with Serbia.
Several other countries have tightened their border controls, including Germany, Austria and the Netherlands.