LONDON (Reuters) - Prime Minister Theresa May discussed defence, security and trade with Polish Prime Minister Beata Szydlo on Monday as Britain looks to strengthen ties with a key ally before it leaves the European Union.

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The summit, attended by several senior ministers from both countries, focussed on the bilateral relationship rather than Brexit negotiations but May also updated her Polish counterpart on Britain’s preparations.

“The UK and Poland have been close allies in the EU and we plan to be even closer allies once the UK has left,” May told a news conference following the meeting.

May, who plans to kick off two years of divorce talks with the EU before the end of March, said Britain had made significant progress on preparing for those negotiations since her last meeting with Szydlo in July.

She reiterated her plan to guarantee the post-Brexit rights of the 3 million EU nationals in Britain, as long as the 1 million Britons living in the EU are given the same treatment, and said she hoped an early agreement could be reached on this.

There were an estimated 831,000 Poles in 2015, an increase of 750,000 on the number in 2004, according to Britain’s Office for National Statistics, and there has been a spate of xenophobic attacks on them since Britain’s June Brexit vote.

Szydlo said the rights of its citizens living in Britain was Poland’s top priority for Brexit, but discussions on this would take place after the formal exit process has begun.

“Together we have to reach in negotiations solutions that will be most beneficial, and most of all acceptable, for both EU citizens ... as well as for British citizens. These negotiations will be held between the EU and Britain,” Szydlo said.

Poland joined the European Union in 2004 and has been one of Britain’s closest allies in calling for reform of the bloc.

Szydlo’s government has seen Britain as a focus of its foreign policy in the EU since it came to power last year, in contrast to the previous centrist cabinet’s emphasis on Germany.

“The United Kingdom is a strategic partner for Poland and I deeply believe that we will deepen our relations in the coming months and years,” she told the news conference.

May said as part of its Brexit negotiations, Britain would have to look at justice and home affairs arrangements it had entered into as part of its membership of the EU, such as European policing agency Europol.

The two leaders also discussed their commitment to NATO, and May said Britain would deploy 150 troops and several armoured vehicles to north east Poland in April next year to deter Russian aggression by helping secure NATO’s eastern flank.

“We have agreed to work towards the first UK-Poland bilateral defence treaty and to strengthen ties between our defence industries,” she added.