PESHAWAR At least 21 persons were killed when an unmanned US drone fired four missiles on a vehicle and a suspected compound separately in Sheratlan area of Mir Ali, North Waziristan Agency on Monday. Sources said that the spy planes remained hovering over the area after the attack, bringing the relief activities being carried out to retrieve the victims to a halt. The consecutive drone attacks caused fear and panic among the residents, as three more drone were hovering over the same location. It was not conformed that whether or not the killed persons were militants. However, fifteen persons were reportedly killed in the attack. The identity of the victims could not be ascertained, however, the officials believed that most of them were Pakistani. The Mir Ali is believed to be a Talibans stronghold. According to the initial reports a compound was hit but later on it was confirmed that a vehicle was also hit, said a Pakistani security official. Both the targets were in Mir Ali, he added. It may be mentioned here that drones have killed scores of militants as well as innocent people so far. Though Pakistan authorities have several times protested against the violation of Pakistani airspace, the US has been terming the attacks more effective against Taliban. Agencies add: US missiles killed at least 21 militants in northwestern tribal belt where the United Nations said Monday it was suspending food handouts in one district after a suicide attack. The missiles destroyed a vehicle and compound in North Waziristan, reputedly the countrys most impregnable Taliban and Al-Qaeda fortress. Local security officials said unmanned US aircraft struck Mir Ali village, 25 kilometres east of Miranshah, the tribal districts main town. Both the targets were in Mir Ali and hit almost back to back. We have reports of 18 militants death, but can confirm only 15 at the moment, he said. Intelligence officials in Miranshah put the death toll as high as 21 and said that two vehicles were destroyed by four missiles fired from US drones. The United States does not confirm drone attacks, but its military and the Central Intelligence Agency operating in Afghanistan are the only forces that deploy the aircraft in the region. The covert campaign has doubled missile attacks in the tribal area this year where around 100 drone strikes have killed more than 640 people since January 1, compared to 45 killing 420 people in 2009. Around 4,000 people have died in suicide and bomb attacks across Pakistan since government forces raided Lal Masjid in Islamabad in 2007. The attacks have been blamed on networks linked to the Taliban and Al-Qaeda. Ahmad Nabi from Khyber Agency adds: Meanwhile, the US-led allied forces, stationed in Afghanistan, violated Pakistans air space again on Monday when its helicopters entered Khyber Agency, official sources informed. At about 09:30 a.m. two gunship helicopters entered Pakistani territory and continued lower flights for five minutes, hovering over the border town of Torkham, Bachamena, and other adjacent areas, and returned back to their base somewhere in Afghanistan, sources told. In the meantime two drones were also seen over Tirah Valley, local sources confirmed. The movement of drones spread wide fear and panic among the people. It is pertinent to mention here that in the last week drone strikes in the area killed 54 suspected militants including prominent leaders of LI and TTP. Our staff reporter from Islamabad adds: US Embassy rejected media reports that the NATO helicopters violated Pakistani airspace near Torkham on Monday. This is not the case. US Embassy officials confirmed with NATO commanders in Kabul that no NATO helicopters crossed the border into Pakistan, said a US Embassy press note issued here Monday. Furthermore, all Coalition and US air operations in Afghanistan conducted along the Afghanistan-Pakistan border region are closely coordinated with Pakistans Air Force. We refer all questions concerning the integrity of Pakistani airspace to the Pakistan Air Force, it concluded.