A big leap in immigration from outside the EU is evidence of the strength of the UK economy, Theresa May says.

The prime minister appeared relaxed about the increase – to its highest level for 15 years – while insisting she remained committed to slashing numbers to “the tens of thousands”.

The latest figures show 283,000 more people moved to the UK than left the country in the year to last September – almost three times the government target of 100,000.

The rise was fuelled by 261,000 non-EU arrivals, the highest figure since 2004, outweighing a fall in EU net migration to the lowest level since 2009.

Ms May has fought almost a lone battle in cabinet to keep the long-missed target, having made cutting the numbers of migrants her priority as home secretary.

However, asked for a response, her official spokesman said: “What the figures show you is that the UK is continuing to attract and retain highly-skilled workers, including more doctors and nurses, while talented international students are benefiting from our world-leading universities and boosting our economy.”

The relaxed comments come despite the pressure group Migration Watch, long an influence on Tory policy, describing the increase as “a real concern”.

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The spokesman added: “We will continue to reform routes from outside Europe as we build a new immigration system that works in the best interests of the country

“And, as you know, we are committed to reducing immigration to sustainable levels and that means the tens of thousands.”

Meanwhile, Diane Abbott, Labour’s shadow home secretary, condemned the government’s failure to drop the target, saying: “Its policy is not really about reducing numbers, but allows it to maintain a constant campaign against migration and migrants.”

The Office for National Statistics (ONS) said fewer people were arriving for work, but more for study with non-EU student immigration at its highest level since 2011.

However, the prime minister’s spokesman said it was partly explained by a decision to recruit badly-needed NHS staff.

“There was a decision taken last year to address particular concerns around the health service to allow in more skilled doctors and nurses, and you obviously can see aspects of that in the figures published today,” he said.

On the increase in foreign students, the spokesman said: “It's always been the case that there is no cap on the number of students who can come to the UK.

“We have very successful universities which are renowned internationally. Students are coming to attend those universities, but obviously they go home at the end of those courses in the vast majority of cases.”

He insisted Ms May had always argued it would “take time” to achieve the target of net migration below 100,000, adding: “We are taking steps to deliver upon that.”

Meanwhile, overall EU net migration stood at 57,000 after 145,000 European citizens left and 202,000 arrived.

People from EU8 countries, including Poland, Slovakia, Lithuania and Hungary, left in the highest numbers, with 53,000 departing during the year.