In this photo made available from The UK Parliament, Britain's Prime Minister Boris Johnson, reacts as he gives an answer during the weekly Prime Minister's Questions session in the House of Commons parliament in London, Wednesday Feb. 12, 2020. Behind from right, Priti Patel, Jacob Rees-Mogg, Mark Spencer. (Jessica Taylor/House of Commons via AP)

LONDON (AP) — British Prime Minister Boris Johnson shook up his government on Thursday, firing and appointing ministers to key Cabinet posts.

Johnson was aiming to tighten his grip on the government after winning a big parliamentary majority in December’s election. That victory allowed Johnson to take Britain out of the European Union last month, delivering on his key election promise.

Now his Conservative administration faces the even bigger challenge of negotiating a new relationship with the 27-nation EU by the end of this year. The two sides are aiming to have a deal covering trade, security and other areas in place by the time a post-Brexit transition period ends on Dec. 31.

So far, the two sides are far apart in their demands. And even with a deal, the U.K. faces a huge adjustment when decades of seamless trade and travel with the EU end at the start of 2021.

Johnson began his Cabinet shuffle by firing Northern Ireland Secretary Julian Smith — a surprise move. Smith had been widely praised for helping to end the political deadlock that left Northern Ireland without a regional government and assembly for three years. After pressure from the British and Irish governments, the main Irish nationalist and British unionist power-sharing parties returned to work last month.

As well as shuffling his Cabinet, Johnson needs to appoint a new leader for the U.N. climate change conference that Britain is due to host later this year. The summit, known as the 26th Conference of the Parties, or COP26, is scheduled to be held in Glasgow in November.

Planning has got off to a rocky start, with Johnson last week firing Claire O’Neill, a former British government minister appointed last year to head up the event.