England captain Jos Buttler said the defending champions must show their resolve and believe they can turn their faltering World Cup campaign around after a shock 69-run defeat by Afghanistan on Sunday.

A first loss to Afghanistan in any format left England with only one win from their first three matches in the tournament and with little room for error in their remaining six group games.

Afghanistan punished a slack bowling display to reach 284 all out before dismissing England for 215. Harry Brook was the only batsman to offer much resistance as he top-scored with 66.

"It's a big setback obviously. Before the tournament starts you have a different idea of how the first three games would pan out," said Buttler.

"We've got to show a lot of character, a lot of resilience within the team and most of all a lot of belief.

"There was a lot of excellent players in there and we haven't played well enough today but we must keep that belief."

He added: "It's not been the way we wanted to start the competition, but this is the situation we find ourselves in and we're going to have to play some of our best cricket moving forward."

A wayward first ball from Chris Woakes, which Buttler allowed through his grasp for five wides, was a sign of things to come for England.

Afghanistan put on an opening stand on 114 -- thanks in large part to Rahmanullah Gurbaz's swashbuckling 80 -- but slid to 190-6 before Ikram Alikhil's 58 gave them a decent target to defend.

- Tough fixtures still to come -

England lost wickets regularly -- spinners Mujeeb Ur Rahman and Rashid Khan took three apiece -- and their flickering hopes were all but extinguished when Brook departed to leave his team 169-8.

"I'm really disappointed. We've come here wanting to put in a really good performance. We got outplayed today. Afghanistan were fully deserving in their victory," said Buttler.

England play in-form South Africa next on Saturday in Mumbai. They also still have to face tournament favourites and hosts India, Pakistan and five-time champions Australia.

"I think everyone will be disappointed in the dressing room and sort of let that sink in," said Buttler.

"But there's a lot of guys who've been through lots in their career in there as well and guys who've come back from tough situations and shown a lot of character and resilience.

"And it's a very tight-knit group, so we'll get around each other and pick each other up and dust ourselves down and go again."

Ben Stokes has yet to feature after sitting out the opening games with a hip injury, and Buttler gave little away about the health of England's star batsman.

"He wasn't fit for this game but we'll see how he pulls up for the next one," he said.

Buttler also spoke up in defence of Woakes, England's Ashes hero who has struggled to find his rhythm with the new ball to start the tournament.

Woakes has taken just two wickets so far -- both in the win over Bangladesh -- and conceded 7.5 runs an over.

"He's probably not performed as we know he can but he's a class player, he's been the leader of our attack for a very long time," said Buttler.

"He's performed extremely well over a long period of time and they're the guys you want in your team and you keep backing them."