Islamabad , Pakistan ( CNN ) -- Two suspected U.S. drone strikes in Pakistan 's tribal region killed 21 alleged militants Tuesday , intelligence officials said . Two Pakistani intelligence officials said one suspected drone fired four missiles , killing 13 people at an alleged militant hideout in the area of Shawal in South Waziristan , one of the seven districts of Pakistan 's volatile tribal region bordering Afghanistan . The second strike occurred hours later on another suspected militant hideout in North Waziristan . Eight people were killed , the officials said . The officials asked not to be named because they were not authorized to speak to the media . On Monday , a similar attack killed 10 suspected militants in North Waziristan . The overwhelming majority of drone strikes have targeted areas in North and South Waziristan . Analysts say the areas are havens for militants fueling the insurgencies in Pakistan and Afghanistan . The United States does not comment on suspected drone strikes . But it is the only country in the region known to have the ability to launch missiles from drones -- which are controlled remotely . Journalist Saboor Khattak contributed to this report .
NEW : Second suspected drone strike kills 8 , officials say . The overwhelming majority of strikes have targeted North and South Waziristan . The United States does not comment on suspected drone strikes .