text: The 35-year-old skippered the Bears to One-Day Cup victory in September 2016, but less than 12 months on the county are bottom of the Division One Championship table.
  Bell, who last played for England in November 2015, was was recently left out of the Bears' T20 side.
  "This is the right time for me to stand down," Bell said.
  "As a senior player, I will support the team in all ways possible and I believe that our squad has very exciting times ahead.
  "It's been an absolute honour to lead my home county over the last 18 months and my decision to stand down is something that I have thought long and hard about over a period of weeks."
  Bell is to be replaced by former England batsman Jonathan Trott as captain of Warwickshire's Championship side.
  The county's sports director Ashley Giles said Bell made a "brave" decision to focus on batting.
  "Having him focused solely on scoring runs for Warwickshire and Birmingham Bears is a huge asset to the club," Giles said.
  Warwickshire, who won limited-overs silverware in Bell's first season as captain, are in Division One relegation trouble, having lost five of their nine matches - four of them by an innings.
  Bell, the most capped international in Warwickshire history, having played 118 Tests, 161 one-day internationals and eight T20 matches, has scored 345 runs from 14 innings, at an average of 24.64. He has not made a Championship century since April 2016.
  In the T20 Blast, he has hit 251 runs in 12 matches at a strike rate of 117.29, but he was dropped down the order after a run of poor scores at opener.
  Having not batted at all in the Bears' penultimate game, he was left out altogether for the final group game on Friday, which the Bears won against Lancashire at Old Trafford to secure a place in the quarter-finals.
  New Zealand international Grant Elliott captained the side and will be expected to so again for this Friday's last-eight tie against Surrey at The Oval.
  Bell, who was part of the Birmingham Bears T20 Blast title-winning side in 2014, also won the Big Bash in Australia last winter with Perth Scorchers.
target: Ian Bell has stepped down as captain of Warwickshire in all formats of the game to focus on batting.