WASHINGTON ( CNN ) -- Defense Secretary Robert Gates is expected to approve sending thousands of additional forces to Afghanistan to deal with the growing threat from roadside bombs , Pentagon spokesman Geoff Morrell said Friday . Marines detonate a roadside bomb . Injuries from the bombs have increased 700 percent in two years . Over the past two weeks , Gates has concluded that there are not enough forces or equipment in Afghanistan to protect U.S. troops from the threat of roadside bombs , Morrell said . The secretary , he said , wants to send these forces `` as soon as possible . '' Morrell said the deployment would be separate from any that might be requested by Gen. Stanley McChrystal . The plan could send nearly 3,000 troops , another U.S. military official familiar with the proposal said . He said Pentagon planners have already identified some of the units that would be sent . This official asked not to be identified because no final decision has been announced . Plans have been in place to set the U.S. troop level in Afghanistan at 68,000 since earlier this year , when President Obama approved an additional 21,000 troops . The decision comes at a sensitive time politically . In the last few days , two key Democrats have questioned sending additional troops . `` I do n't think there 's a great deal of support for sending more troops to Afghanistan in the country or in Congress , '' Speaker of the House Nancy Pelosi , D-California , told reporters Thursday . On Friday , Sen. Carl Levin , the head of the Senate Armed Services Committee who has recently returned from Afghanistan , said the emphasis should be on training and increasing the size of the Afghanistan army before considering more U.S. forces . `` Our primary goal should be to strengthen the Afghan army and the police , to provide the necessary training and equipment and also to see if we ca n't reintegrate some of the lower-level Taliban people , who are the young people who are n't the religious zealots but are being taken advantage of by the leaders , '' Levin , D-Michigan , told MSNBC . Gates himself has been a vocal opponent of expanding the U.S. presence for fear that the forces would be seen as occupiers by the Afghan population . But last week , he softened that position , saying McChrystal had made a persuasive argument that the concern should not be on the size of the forces but on their conduct . Morrell said the proposal may not raise total U.S. troop strength above 68,000 , because some of the units already scheduled to go could be sent not fully staffed or others already there could be sent home . Still , `` the secretary has already determined this is a requirement that needs to be fulfilled , '' Morrell said . `` The forces there now require more IED protection . '' The troops would specialize in route clearance , explosive ordnance disposal , medical treatment and intelligence-gathering , Morrell said . `` We owe this to the troops already committed to the fight , '' he said . Since 2007 , the number of roadside bombs in Afghanistan has jumped 350 percent , according to the Defense Department . Though many are found before they detonate , the number of troops killed has increased by more than 400 percent and the number wounded is up more 700 percent over the last two years . One U.S. military source told CNN that the Taliban 's capacity to manufacture bombs , train attackers and target U.S. troops has grown over the past year . On September 8 near Kandahar , troops seized five tons of ammonium nitrate , more than twice the amount used in the bombing of the federal building in Oklahoma City , Oklahoma , in 1995 . On August 27 , C-4 plastic explosives were found in Herat by Afghan troops . Afghanistan 's rugged terrain and dirt roads make it easy to quickly hide roadside bombs . `` You have disturbed earth all the time , '' said Gen. Montgomery Meigs , former head of the Department of Defense 's IED Task Force . `` Especially close to villages and close to intersections -- that just makes the seeing and finding , even by soldiers ' eyes , a lot more complicated . '' The Taliban have proven adept at adjusting their strategy as circumstances change . Seeing that troops were routinely stopping ahead of culverts to search for bombs that could be hidden under the roads , insurgents have started placing the bombs ahead of the culverts .
Defense secretary finds not enough forces in Afghanistan to protect U.S. troops . Plan could send nearly 3,000 troops , source says . Comment: Troops killed by roadside bombs up more than 400 percent in 2 years .