WASHINGTON — President Barack Obama on Thursday tried to regain Americans' sinking confidence in his response to the oil spill in the Gulf of Mexico, saying "from the moment this disaster began the federal government has been in charge of the response effort."

"Those who think that we were either slow on our response or lacked urgency don't know the facts," the president said at a midday conference from the East Room of the White House, five weeks after the April 20 explosion of the Deepwater Horizon and the April 22 sinking of the rig. "This has been our highest priority since this crisis occurred."

Obama, facing tough questions, said BP is the responsible party but added, "Make no mistake: BP is operating at our direction." If the federal government orders BP to follow a certain approach, he said, "They are legally bound to do it."

The president also formally announced his administration is suspending the planned exploration of two locations off the Alaskan coast; canceling a pending lease sale in the Gulf of Mexico and a proposed lease sale off the Virginia coast; continuing the existing moratorium and suspending new deepwater well permit issuing for six months; and suspending action on 33 deepwater exploratory wells being drilled in the Gulf of Mexico.

Obama's decision to hold a full-blown news conference, a format he dislikes, comes under intense political pressure for the president, even as BP's latest effort to plug the spill, using a technique known as "top kill," is going forward.

He said his administration's response has not been perfected. Among other critiques, he said, "It took too long for us to stand up our flow tracking group" to estimate the rate of the spill. However, he defended his attentiveness and involvement.

"We understood from day one the potential enormity of this crisis and acted accordingly. The challenge we have is that we have not seen a leak like this before. People are going to be frustrated until it stops and I understand that."