The top US transportation security official has said he has decided not to permit passengers to carry small knives on airplanes.

The announcement came after widespread criticism from flight attendants and the public that easing restrictions would increase flight dangers.

Transportation Security Administration head John Pistole had proposed to loosen rules put in place in the wake of the September 2001 plane hijackings.

But he has now said he would scrap the changes.

"After extensive engagement with the Aviation Security Advisory Committee, law enforcement officials, passenger advocates, and other important stakeholders, TSA will continue to enforce the current prohibited items list," Mr Pistole said.

Hijackers in the 9/11 attacks used small knives to attack crew members and gain control of aircraft.

Cockpits on commercial planes have since been required to have locked doors during flights.

In March, the TSA said that effective 25 April, it would allow knives with blades that are 6cm or less to be carried onto airplanes.

The proposed rules would also have allowed passengers to carry on hockey sticks, golf clubs or billiard cues.

Just days before the rules were due to go into effect, the TSA delayed the change.

Now, six weeks later, Mr Pistole announced he would scrap the proposed rules altogether.

Flight attendants, who had mobilised a massive campaign and started a legal battle to keep the knives off airplanes, applauded Mr Pistole for reversing course and for taking time to hear their concerns.

"Terrorists armed only with knives killed thousands of Americans on 9/11/2001.

"As the women and men on the front lines in the air, we vowed to do everything in our power to protect passengers and flight crews from harm and prevent that type of atrocity from happening ever again," the 90,000-member Flight Attendants Union Coalition said in a statement.

"The TSA was created because of small blades and blades have no place on the airplane. Now we'll make sure that those weapons are never allowed on our airplanes," said Sara Nelson, international vice president of the Association of Flight Attendants.

During a congressional hearing in March, Mr Pistole had defended the rule changes, saying the TSA was facing budget cuts and needed to prioritise threats.

He said the agency finds about 2,000 small pocket knives at checkpoints each day and each one takes about two to three minutes to find and confiscate.

That time could be used looking for more lethal weapons such as non-metallic explosives devices, he said.

But politicians expressed outrage at the plan to ease up on the rules, saying small knives and items such as hockey sticks and golf clubs could cause serious harm in the confined areas of airplane cabins.