US Secretary of State Condoleezza Rice met with her Polish counterpart, Radoslaw Sikorski, on Monday seeking to break the impasse in negotiations for basing a missile-defence system in the Eastern European country, dpa reported.
US State Department spokesman Sean McCormack would not rule out the possibility negotations could be completed this week, when Rice will be in Prague to sign an agreement with the Czech Republic for hosting the system's radar.
"We didn't conclude them in time for the beginning of the secretary's travel," he said. "That doesn't mean we're not going to keep working on them."
Rice will also visit Bulgaria and Georgia on the trip that concludes Thursday.
Poland has rejected as insufficient a US offer to modernize its military and air defences and has tied the issue to any decision to allow the deployment of 10 interceptor missiles on its soil.
The United States wants to field in the system in Eastern Europe to fend off the threat posed by Iran's growing ballistic missile capabilities.
Russia strongly opposes placing the US system in Europe and has threatened to target the bases. Washington has dismissed Russia's objections, saying the system is much too small to jeopardize Moscow strategic nuclear missile fleet.