QUETTA, Pakistan, (Reuters) – A suicide bomber  struck a rally in the Pakistani city of Quetta yesterday,  killing at least 54 people in the second major attack this week  and piling pressure on a U.S.-backed government overwhelmed by  a flood crisis.

Pakistan’s Taliban claimed responsibility for the blast and  said it would launch attacks in the United States and Europe  “very soon” — repeating a threat to strike Western targets in  response to drone attacks that have targeted its leadership.

In Washington, the White House condemned the Quetta attack  on a Shi’ite rally expressing solidarity with the Palestinian  people, saying it was “even more reprehensible” because it came  during the Muslim holy month of Ramadan as Pakistan reels from  disastrous flooding.

A U.S. counterterrorism official said the threat by the al  Qaeda-linked Taliban against the United States and Europe could  not be discounted.

The attack came just two days after Washington added the  Pakistani Taliban to its list of “foreign terrorist  organizations” and charged its leader, Hakimullah Mehsud, with  plotting a bombing that killed seven CIA agents at a U.S. base  in Afghanistan last December.

In Quetta, dozens of dead and wounded people lay in pools  of blood as fires engulfed vehicles. Senior police official  Hamid Shakeel told Reuters at least 54 people were killed and  about 160 wounded.

Hours later, the Taliban said the bombing was revenge for  the killing of radical Sunni clerics by Shi’ites, further  challenging Pakistan’s unpopular civilian government.

“We take pride in taking responsibility for the Quetta  attack,” Qari Hussain Mehsud, a senior Pakistani Taliban and  mentor of suicide bombers, told Reuters.

Earlier in the day, the Taliban also claimed responsibility  for bombings on Wednesday at a Shi’ite procession in the  eastern city of Lahore in which at least 33 people died.

Those blasts were the first major attack since the worst  floods in Pakistan’s history began more than a month ago. The  Taliban and its allies often target religious minorities in a  campaign to destabilize the government.

Aside from its battles against homegrown Taliban, Pakistan  is under intense American pressure to tackle Afghan Taliban  fighters who cross the border into Pakistan’s lawless tribal  areas to attack U.S.-led NATO troops.

The United States has stepped up missile strikes by  pilotless drone aircraft against militant targets in Pakistan’s  Pashtun tribal lands since the start of 2010.

Yesterday, U.S. drones fired missiles at two targets in the  North Waziristan tribal region, killing seven militants,  including two foreigners, intelligence officials said.

Pakistan’s Taliban has responded to drone attacks by saying  it would strike Western targets.

“We will launch attacks in America and Europe very soon,”  Mehsud told Reuters by telephone on Friday from an undisclosed  location.

The group claimed responsibility for a failed bomb plot in  New York’s Times Square in May and, in December 2009, a Spanish  court jailed 10 Pakistanis and an Indian for attempted suicide  bombings on Barcelona’s metro in 2008, saying they were  inspired by the Pakistan Taliban’s then leader.