Defense Secretary Chuck Hagel is hinting at growing U.S. impatience with Afghan President Hamid Karzai for not signing an accord permitting American troops to remain in his country after the U.S. combat mission ends in December.

Hagel told reporters flying with him to Poland Thursday that at some point Karzai's indecision will collide with Washington's need to plan the post-2014 military mission that Karzai himself has said he favors.

Hagel said he respects Karzai's right to decide the matter as he sees fit. And he said the U.S. has a limited ability to influence the Afghan leader.

Hagel was visiting Warsaw to consult with Polish officials on Afghanistan and other security issues.