ISLAMABAD -- A large crowd of Islamic militants rallied this week in the heart of Islamabad to voice support for Pakistan's army and to condemn the United States in another sign of a growing tide of extremism sweeping the country.

The Thursday rally by Sipah-e-Sahaba Pakistan, a violent group considered close to al-Qaida that has been banned by Pakistani authorities, was followed Friday by protests in several Pakistani cities against the death sentence handed down a week ago to an extremist who earlier this year gunned down a senior Pakistani official whom he'd accused of blasphemy.

The new evidence of rising Islamic extremism comes as the United States and Afghanistan accuse Pakistan's military and its main spy agency of supporting jihadist groups - even as extremist violence besieges Pakistan.

Pakistani police patrolled Thursday's rally, which was held in a field hockey stadium and attended by between 5,000 and 10,000 people, according to witnesses, but made no effort to break it up. The group was using its new name, Ahle Sunnat wal Jamaat, but did little to hide its true identity, plastering the stadium with Sipah-e-Sahaba posters while speakers paid homage to the group's former leaders.

Addressing the gathering, Ahmed Ludhianvi, who's considered the head of Sipah-e-Sahaba, pledged to back Pakistan's military and its chief, Gen. Ashfaq Kayani.

"Because of threats from America and conspiracies against Pakistan, I promise to give Gen. Ashfaq Kayani 100,000 of our followers as fighters," he said.

The event was held in the Aabpara commercial district in central Islamabad, just about half a mile from the headquarters of the country's Inter-Services Intelligence Directorate spy agency.

Last month, Adm. Mike Mullen, the outgoing chairman of the U.S. Joint Chiefs of Staff, claimed that a deadly Afghan insurgent group, the Haqqani network, was a "veritable arm" of the ISI, which is part of the military. Pakistan vehemently denies patronizing Haqqani or other jihadist groups.

The resolutions agreed to at the rally, written copies of which were handed out, included expelling the U.S. ambassador and ending Pakistani military operations against extremists in its northwest. There were also many resolutions against Pakistan's Shiite minority and Iran, along with chants of "Shiites are infidels."

Sipah-e-Sahaba started out as a murderous anti-Shiite group in the 1980s, when the military was supporting hard-line Sunni Muslim organizations in reaction to the revolution in Shiite Iran. But the group now has a broader extremist agenda, including links with the Pakistani Taliban. Its offshoot, Lashkar-e-Jhangvi, is considered one of the most dangerous terrorist groups in the country.

Militant groups regularly change their names to escape bans, a remarkably easy ploy.

An Islamabad city official, who spoke on the condition of anonymity because of the sensitivity of the issue, said that because Ahle Sunnat wal Jamaat was not a banned group, it could not be stopped from holding the rally.

Separately, after the weekly prayers Friday, demonstrations were held in several cities, including Rawalpindi, where Pakistan's military is headquartered, and Lahore, against the death sentence handed down by a court last weekend to Mumtaz Qadri, a police commando who in January shot dead Salman Taseer, who was governor of Punjab province.

Taseer had spoken out against the country's blasphemy law, which has been used to prosecute Christians and members of other religions for alleged insults to Islam.

An angry mob of several hundred congregated in Rawalpindi, Qadri's hometown, next to Islamabad, throwing rocks and blocking a major road. In Lahore, the provincial capital of Punjab, about 2,000 people chanting slogans gathered in the center of the city.

(Shah is a McClatchy Newspapers special correspondent.)