Missile attacks by US drones in Pakistan's tribal areas have more than doubled under the Obama administration, research by the BBC Urdu service shows.

Compared with 25 drone strikes between January 2008 and January 2009, there were at least 87 such attacks between President Obama taking office on 20 January 2009 and the end of June 2010.

More than 700 people have been killed in such attacks under Mr Obama, compared with slightly fewer than 200 from under his predecessor, George W Bush.

The militant backlash over the same period has been even more violent. Extremists have struck more than 140 times in various Pakistani locations, killing more than 1,700 people and injuring hundreds more, the BBC research shows.

Continue reading the main story Ten cities worst hit by militant attacks Location No of Deaths Peshawar 362 Lahore 253 Khyber 120 Rawalpindi 98 Lakki Marwat 93 Kohat 91 Dera Ismail Khan 77 Lower Dir 75 Karachi 69 Dera Ghazi Khan 50 Source: BBC Urdu service. Data from Jan 2009 to June 2010

While attacks by militants cannot be described as direct retaliation for drone strikes, they are firmly part of the battle the US and Pakistani authorities are fighting against radical Islam's operational bases in Pakistan.

Over the same 18-month period, many more than 2,500 people have died in offensives by the Pakistani army and fighting between troops and militants. Exact figures are impossible to obtain.

Places such as Swat and South Waziristan which have seen offensives by the Pakistani military are virtually closed to independent media and other groups.

The increased frequency of drone strikes follows a reported shift in US policy to extend its drone operations. It has moved from targeting al-Qaeda suspects to including Pakistani Taliban who are believed to be providing a haven for al-Qaeda leaders and operatives.

The bulk of these attacks have been in North Waziristan, with neighbouring South Waziristan the next main target.

While more than 700 people have died in these attacks, positive identification of the victims, either by Pakistani or US authorities, has been made in fewer than a dozen instances.

Continue reading the main story Areas hit by drone attacks Province No of deaths South Waziristan 279 North Waziristan 386 Bajaur 14 Bannu 5 Orakzai 8 Kurram 54 Source: BBC Urdu service. Data from Jan 2009 to June 2010

There have been notable successes for the Americans and Pakistanis, including the killing of Taliban militant leader Baitullah Mehsud last August and several people described as senior al-Qaeda leaders.

The data collected by the BBC Urdu service shows militant attacks dipping when Mehsud was killed and then peaking last autumn when Pakistani troops launched the South Waziristan offensive. Drone attacks reached a high when the operation was declared over and the Pakistani army refused to push on into North Waziristan as the US government wanted it to.

Pakistan has consistently argued that drone attacks are hindering rather than helping with the battle against extremism, saying they fuel public anger against the government and the US and boost support for militants.

On the other hand, the US, which does not routinely confirm drone operations, has always implied there is a tacit understanding between the two countries over the attacks.

The CIA declined to comment for this story.

The Taliban say drone attacks make them more determined to fight, but admit that they have disrupted their operations.

This data was compiled between January 2009 and July 2010 by the BBC Urdu service. It is based on reports from BBC World Service correspondents working in Northern Pakistan and the tribal areas.