Washington, May 13 (IANS) US President Barack Obama has warned Pakistan that his administration would not allow "safe havens" for militants in its tribal region bordering Afghanistan or let Osama bin Laden operate with impunity.

"My bottom line is that we cannot allow Al Qaeda to operate," he said. "We cannot have those safe havens in that region," he said Wednesday at a joint White House news conference with Afghan President Hamid Karzai.

"I'm not going to allow Al Qaeda or Osama bin Laden to operate with impunity, planning attacks on the US homeland," he said, adding his envoy to the region, Richard Holbrooke, will convey his message to Islamabad.

"We're going to have to work both smartly and effectively, but with consistency in order to make sure that those safe havens don't exist."

Obama said he had appointed Holbrooke as a special envoy for Pakistan and Afghanistan to give a new focus to dealings with terrorism.

"I've sent over Richard Holbrooke - one of our top diplomats - to evaluate a regional approach," he said. "We are going to need more effective coordination of our military efforts with diplomatic efforts, with development efforts, with more effective coordination with our allies in order for us to be successful."

Obama said he had no schedule for the withdrawal of US troops from Afghanistan.

"I do not have yet a timetable for how long that's going to take..."