WASHINGTON: The Pentagon said that arriving of the Uzbec, Chechan and Arab terrorist attackers in Afghanistan from Pakistan is a grave concern for the United States of America.n nUS commanders in Afghanistan have requested three more combat brigades, or about 10,000 troops, to deal with growing insurgent violence in the eastern and southern parts of the country but the Pentagon is unable to send additional combat brigades to Afghanistan this year because of constraints imposed by the war in Iraq, leaving the decision on reinforcements to the next president, a spokesman said Wednesday.n nGeoff Morrell, the Pentagon spokesman, said Iraq remains the top priority for the Bush administration, which places limits on the forces available for duty in Afghanistan over the short term. n n"Obviously we don't have the means to send three BCTs (brigade combat teams) to Afghanistan at this very moment, without making some very hard choices," he said.