Pakistan captain Mohammad Hafeez admitted his faltering pace bowlers were a concern ahead of the Super Eights round where big teams can capitalise on their weakness.
Pakistan thumped Bangladesh by eight wickets in Pallekele on Tuesday, with Imran Nazir hitting a career best 72 as Pakistan comfortably chased down a 176-run target with eight balls to spare in the group D match.
But they head into the next round with a question mark on their pace bowlers, with experienced Umar Gul conceding 43 off his three overs and Sohail Tanveer going for 25 in his three.
Pakistan faces explosive matches against formidable South Africa (Friday), arch-rivals India (Sunday) and Australia (Tuesday) in Colombo, and Hafeez said their fast bowling needed a lift.
"Yes, there is a bit of concern as a captain. Our fast bowlers are not producing in the manner that they can," Hafeez said after the match. "We expect Colombo pitch to turn a bit more, these pitches (here) were slightly different."
Gul, joint second wicket-taker with team-mate Shahid Afridi with 60, went for 39 in his three overs during Pakistan's 13-run win over New Zealand in the first game.
Hafeez said he believed Gul will stage a comeback quickly.
"Gul is a good bowler and has bowled well in limited overs cricket, so I hope he will improve in the next matches," said Hafeez, who promised no let-up in the next round.
"We know that every team can beat anyone else in T20. We aren't going to relax even a little bit. We know we have to work hard," said Hafeez, who praised a complete team effort in all matches.
"The best thing is that whatever role we assign to players they're putting in maximum effort to do the job. All 15 in our squad are match winners and this team is united in trying to do the best for Pakistan," said Hafeez.
Pakistan finished runners-up to India in the inaugural World Twenty20 held in South Africa in 2007 before winning the next, held in England two years later.
They were losing semi-finalists in the last World Twenty20 held in the Caribbean in 2010.