The 32-year-old batsman retired from one-day international cricket in May, citing the intensity of the schedule and the physical demands on him, but remains available to play Tests for England.
He has been selected for the first Test against South Africa due to begin on Thursday at The Oval.
Media reports in Britain over the weekend suggested Pietersen was willing to make a return to all three formats, but only if the ECB allowed him to play out the upcoming Indian Premier League (IPL) season with his side Delhi Daredevils.
If the request was granted, Pietersen, who earns a lucrative purse from the IPL, would miss England's two-Test series against New Zealand due to start next May at Lord's.
In June, Pietersen expressed his desire to help England retain their Twenty20 world title in Sri Lanka in September and October.
"If they want me to play the T20 World Cup I'll play it, but contracts are contracts," he said. "I made the decision (to retire) for schedule reasons. I can't carry on doing it all."
England will submit their final squad list of 15 for the Twenty20 World Cup on August 18.
Pietersen was named player of the series when England won the 2010 World Twenty20 tournament in the Caribbean.
The right-hander has an average of 37.93 at Twenty20 level and has scored 1,176 runs.
England squad: Stuart Broad (Nottinghamshire) (Capt), James Anderson (Lancashire), Jonathan Bairstow (Yorkshire), Gareth Batty (Surrey), Ian Bell (Warwickshire), Ravi Bopara (Essex), Scott Borthwick (Durham), Tim Bresnan (Yorkshire), Danny Briggs (Hampshire), Jos Buttler (Somerset), Alastair Cook (Essex), Steven Croft (Lancashire), Steven Davies (Surrey), Jade Dernbach (Surrey), Steven Finn (Middlesex), Alex Hales (Nottinghamshire), Craig Kieswetter (Somerset), Michael Lumb (Nottinghamshire), Stuart Meaker (Surrey), Eoin Morgan (Middlesex), Graham Onions (Durham), Samit Patel (Nottinghamshire), Matt Prior (Sussex), Joe Root (Yorkshire), Ben Stokes (Durham), Graeme Swann (Nottinghamshire), James Taylor (Nottinghamshire), James Tredwell (Kent), Chris Woakes (Warwickshire), Luke Wright (Sussex)