If the Obama administration wants to enter new talks with Iran, that's fine -- but they had better keep ramping up the pressure on the Islamic Republic during negotiations and not trade sanctions for piecemeal concessions from the Iranians, 12 U.S. senators said Wednesday.

"As the P-5+1 prepares to resume talks with Iran, we strongly believe that any hope for diplomatic progress with Iran depends upon a continuing and expanding campaign of U.S. and international pressure on the regime and that such pressure must continue until there is a full and complete resolution of all components of illicit Iranian nuclear activities," said Sens. Bob Menendez (D-NJ), Jim Risch (R-ID), Joe Lieberman (I-CT), John McCain (R-AZ), Richard Blumenthal (D-CT), Kelly Ayotte (R-NH), Kirsten Gillibrand (D-NY), Marco Rubio (R-FL), Ben Cardin (D-MD), Pat Toomey (R-PA), Chuck Schumer (D-NY) and Lindsey Graham (R-SC) in a joint statement Wednesday.

"As we recently wrote to President Obama, we remain extremely concerned that the Iranian government will seek to buy time or otherwise dilute the focus of our diplomacy through proposals that either suspend or reverse the current momentum of the pressure track in exchange for partial measures that fail to address the totality of their nuclear program," the senators' statement continued. "Such tactical maneuverings are a dangerous distraction and should not be tolerated. For instance, we would strongly oppose any proposal that caps or limits sanctions against the Iranian regime in exchange for anything less than full, verifiable, and sustained suspension of all enrichment activities, including both 3 percent and 20 percent enrichment."

When Iran offered to come back to talks last month, these 12 senators were quick to put together a letter outlining their precise concerns and what they wanted to see President Barack Obama's administration do.

In addition to continuing along the pressure track, they want the administration to insist that Iran suspend all enrichment-related and reprocessing activities "for the foreseeable future," cooperate with the International Atomic Energy Agency, and resolve all outstanding questions about military dimensions of its nuclear program. The Obama administration has said repeatedly that Iran has the right to enrich uranium for peaceful purposes, but these 12 senators don't agree.

EU High Representative for Foreign Affairs Catherine Ashton, in her March 6 letter welcoming new talks, acknowledged that the P5+1 countries - Britain, China, France, Russia, the United States, and Germany -- will engage in discussions over confidence-building measures to the Iranian government.

"We remain convinced that initially we could work towards the shared objective to engage in a constructive dialogue on the basis of reciprocity and a step by step approach based on practical and specific suggestions for confidence building measures," she wrote.

But the senators think that is foolish, and want to emphasize that the administration should not trade the relaxation of sanctions for partial measures by the Iranians, which they see as a delaying tactic.

"Such tactical maneuverings are a dangerous distraction and should not be tolerated," the senators wrote. "For instance, we would strongly oppose any proposal that caps or limits sanctions against the Iranian regime in exchange for anything less than full, verifiable, and sustained suspension of all enrichment activities, including both 3 percent and 20 percent enrichment. The time for confidence building measures is over."