Boris Johnson has quit as UK foreign secretary over the prime minister's handling of Brexit.

Johnson failed to turn up for an important European summit he was due to host in London.

"His replacement will be announced shortly," Downing Street said Monday. "The prime minister thanks Boris for his work."

The Labour Party says Theresa May's government is now in "meltdown".

LONDON — Boris Johnson has resigned as UK foreign secretary in a major blow to Prime Minister Theresa May.

"This afternoon, the prime minister accepted the resignation of Boris Johnson as foreign secretary," a representative for May said Monday. "His replacement will be announced shortly. The prime minister thanks Boris for his work."

In a statement to members of Parliament, May paid tribute to Johnson's work as foreign secretary but added that "we do not agree about the best way of delivering our shared vision".

His departure follows shortly after the resignation of his colleague David Davis, who resigned as Brexit secretary on Sunday after also refusing to endorse May's Brexit strategy.

The pound plunged after the news of Johnson's departure was announced, as the future of May's government looked in doubt. Rumours were circulating in Westminster on Monday afternoon of other ministers also considering their position.

Eyebrows were first raised after Johnson failed to appear at the Western Balkans Summit, which he was due to host in London on Monday afternoon.