( CNN ) -- President Obama is `` deeply concerned '' about the growing number of deadly attacks on U.S. forces by Afghan security forces , and plans to contact the Afghan president to discuss taking tougher actions , he said Monday . `` I 'll be reaching out to President ( Hamid ) Karzai , '' Obama told reporters at the White House , adding , `` We 've got to make sure that we 're on top of this . '' Obama spoke Monday with Gen. Martin Dempsey , chairman of the Joint Chiefs of Staff . The top U.S. military official is in Afghanistan for meetings with coalition and Afghan leaders , including Gen. John Allen , commander of NATO forces , and Afghan Army Gen. Sher Mohammad Karimi , Dempsey 's counterpart in the country . There has been some success , including better counterintelligence , Obama said . `` But obviously we 're going to have to do more . '' `` And hopefully over the next several weeks we 'll start seeing better progress on this front , '' he added . An incident Sunday brought the death toll in attacks by Afghan military and police personnel this year to 40 , according to U.S. military officials . Twenty-three of those killed were Americans , according to the U.S. Defense Department . The NATO death toll in what the military is now calling `` insider attacks '' is already higher than it was last year , according to statistics compiled by the New America Foundation , a public policy think tank . NATO 's International Security Assistance Force said Friday that 39 people had been killed in these attacks in 2012 . That was before Sunday 's attack killed one ISAF service member . The exact number of attacks remains unclear . While the U.S. military said there have been 40 insider attacks this year , ISAF tweeted last week that there had been 27 such attacks this year . There have been two more since that tweet . An ISAF spokesman told CNN on Friday there had been 31 such attacks before Sunday 's attack . NATO and the United States say the vast majority of the attacks are not the work of the Taliban or insurgent groups . `` Some 10 % we know are related to the insurgency , '' Brig . Gen. Gunter Katz , a spokesman for the ISAF , said last week . An April report by the U.S. Defense Department said , `` Investigations have determined that a large majority of green-on-blue attacks are not attributable to insurgent infiltration of the ANSF , but are due to isolated personal grievances against coalition personnel . There is no indication that these recent attacks are part of a deliberate effort by insurgents , nor were they coordinated with each other . '' The term `` green-on-blue '' refers to a color coding system used by the military , in which blue refers to the friendly force , in this case ISAF ; and green refers to an allied friendly forces , in this case Afghan National Security Forces . When investigators traveled to the attackers ' home villages to investigate what was known about them , the information they collected led them to believe most of the attackers were generally not aligned with an insurgent group , but had their own grievances , military officials say . But the motivations of about half the attackers are difficult to determine definitively because the perpetrator is dead or has fled , CNN National Security Analyst Peter Bergen and Jennifer Rowland of the New America Foundation write in a column on CNN.com . Some of the incidents appear to have taken place after arguments between Afghan and international troops , the column notes . Last year , U.S. military behavioral scientist Jeffrey Bordin interviewed more than 600 Afghan soldiers and police and found they held overwhelmingly negative perceptions of Western soldiers , stemming from incidents including alleged indiscriminate shootings that killed civilians and the public searching of Afghan soldiers outside NATO bases , as well as U.S. soldiers urinating in public or cursing at their Afghan counterparts , Bergen and Rowland write . `` Another likely cause of the increase in the number of green-on-blue incidents is straightforward : In the past two years the size of the Afghan army and police force has almost doubled from around 200,000 to around 350,000 , '' the column says . Afghan President Hamid Karzai spoke Sunday with U.S. Defense Secretary Leon Panetta . `` They expressed shared concern over this issue and agreed that American and Afghan officials should work even more closely together to minimize the potential for insider attacks in the future , '' Pentagon spokesman George Little said . Dempsey , in a statement Monday , said Karzai 's public statement condemning insider attacks was `` tremendously important , and I hope it permeates to the lowest levels of the Afghan government and military . '' Afghan police are most likely to launch such attacks , Dempsey said . `` The vulnerability of local police to ( terrorist ) influence is great . ... They do n't move around the country the way the Army does , so they live at the point of corruption . I 'm sure that 's the case here too . '' Officials are examining the vetting process for Afghan soldiers and police `` and investigating where it failed , '' a Defense Department statement said . All troops at NATO headquarters and all bases across the country have been ordered to carry loaded weapons around the clock , CNN learned Friday . CNN 's Barbara Starr contributed to this report .
NEW : President Obama says he will talk to President Obama about the issue . NEW : Obama spoke with the chairman of Defense Department , who is in U.S. . 10 % of the attacks are related to the insurgency , military officials say . `` Vulnerability of local police to ( terrorist ) influence is great , '' the Afghanistan top military official says .