Pakistan's army chief is rejecting what he says is “speculative reporting” about a joint military operation with the United States in Pakistan's North Waziristan.

The northwestern tribal agency is a known stronghold of Taliban and al-Qaida-linked militants and U.S. officials have repeatedly called on Pakistan to launch an offensive there. The militant Haqqani network, which is blamed for a number of attacks on U.S. forces in Afghanistan, is believed to be based in North Waziristan.

On Friday, Pakistani General Ashfaq Parvez Kayani released a statement saying he and the head of U.S. CENTCOM, General James Mattis, discussed military cooperation during talks the night before.

Kayani said “we might, if necessary, undertake operations in North Waziristan Agency, in the timeframe of our choosing and determined only by our political and military requirements.”

Pakistan's army chief added that such operations “will never be a result of any outside pressure” and that “Pakistan's national interest continues to be the prime consideration in this regard.”

U.S. Defense Secretary Leon Panetta told the Associated Press earlier this week that Kayani has told U.S. military officials that Pakistan plans to conduct an operation North Waziristan soon.

Separately on Friday, Pakistani authorities say a bomb hit a bus carrying Shi'ite Muslims in the southern city of Karachi, killing at least one person.

The blast comes a day after suspected Sunni militants shot and killed 22 Shi'ites who were traveling on buses in Pakistan's northwestern Mansehra district.

Officials say the bus was carrying Shi'ites on their way to an annual rally marking solidarity with the Palestinians when the bomb exploded in Karachi. At least 11 people were wounded in Friday's blast.