Washington ( CNN ) -- The Obama administration is likely to come under new pressure to take more decisive steps in Syria following opposition claims that Bashar al-Assad 's government used chemical weapons to kill more than 1,000 people . While the regime denied the fresh accusations , the administration said it could not immediately verify the accuracy of newly released videos online purportedly showing civilians suffering from chemical agents outside Damascus . Still , the images were searing and prompted the United States to seek an urgent U.N. investigation , demand accountability , and not rule out additional help . `` There is an investigation team that 's on the ground in Syria right now . And we are hopeful that the Assad regime will follow through on what they have claimed previously , that they are interested in a credible investigation that gets to the bottom of reports that chemical weapons have been used , '' White House spokesman Josh Earnest said . Earnest added the administration has regularly considered increased aid for the rebels . `` The conduct of this investigation , the results of this investigation or the efforts by the Assad regime to inhibit this investigation will certainly impact that calculation about possible additional aid , '' Earnest said . Key questions would immediately surface if the latest troubling development from a region wracked by civil war for more than two years were to change the overall calculus for the United States . What new steps would it take ? How would it address uncertainty about the rebel makeup ? And how would it approach what some believe is a worsening multidimensional trust gap on the issue of rebel assistance ? The administration has rebuffed calls for a stronger military aid response , opting to push for a political solution and provide humanitarian , logistical and limited weaponry and other hardware . Syrian activists : Videos show chemical weapons used . A chief problem has been identifying those rebels the United States would happily deal with vs elements said to be militants , including some with ties to al Qaeda . `` Syria today is not about choosing between two sides but rather about choosing one among many sides , '' Joint Chiefs Chairman Gen. Martin Dempsey wrote this week to Rep. Eliot Engel of New York . `` It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favor . Today , they are not , '' he said in the August 19 letter . Inherent political mistrust amid sharp partisan divisions in Washington coupled with close congressional vetting also have influenced the response to Syria . Congress is currently on vacation until after Labor Day . Also critically , mistrust cuts both ways . According to experts who have traveled to Syria during the war , opposition groups have little faith in the United States . Syrian refugees stream into Iraq . `` Our credibility was n't high to begin with and obviously did n't improve with time , '' said David Lesch , Middle East history professor at Trinity University and author of `` Syria : The Fall of the House of Assad . '' `` They basically shrug their shoulders and say , 'Oh well , what is new ? ' They feel like they are on their own on this . '' Lesch said the administration had not had enough contact with oppositions groups from the outset . `` There is just a lack of knowledge of these groups , '' he said . This is the second time the administration has faced questions about chemical weapons use in Syria . Last August , President Barack Obama said using those weapons would cross a `` red line '' and provoke a U.S. military response . His administration confirmed in June that chemical agents were used in April and it resulted in an uptick of military aid . But the `` red line '' tag has seriously damaged U.S. credibility in the region , said Andrew Tabler , author of `` In the Lion 's Den : An Eyewitness Account of Washington 's Battle with Syria . '' `` Reacting way too late - that has been our policy on Syria for some time , '' Tabler said . `` ( The United States ' credibility is ) very low because of its inability to keep to its word . We have done absolutely nothing to enforce the red line . What kind of signal does that send to the Syrian people ? '' But in his letter , Dempsey warned that even limited military action in Syria could lead to deeper involvement -- a point the military has made previously . The administration has said it has no plans to put `` boots on the ground . '' A team of U.N. chemical weapons inspectors landed in Syria this week to begin probing chemical weapons allegations , and the U.N. Security Council planned a meeting on Wednesday to address the issue . CNN 's Samira Said , Ed Payne , Jessica Yellin , Dana Bash and Chloe Sommers contributed to this report .
NEW : White House wo n't rule out more help for rebels , has n't verified latest claim on chem weapons . Comment: Syrian opposition groups do n't trust the Obama administration , experts on the region say . Distrust stems from the U.S. debate over chemical weapons , likely to reignited after latest claims .