76 senators sign letter demanding Obama take harder line against Iran

Seventy-six senators on Monday signed a letter demanding the Obama administration take a harder line to stop Iran’s nuclear program, including weighing possible military options. 

"We believe our nation must toughen sanctions and reinforce the credibility of our option to use military force at the same time as we fully explore a diplomatic solution to our dispute with Iran," read the letter sent to the White House.

The letter is signed by conservative lawmakers including Sens. Ted CruzTed CruzSenate GOP: National museum should include Clarence Thomas Senate GOP to Obama: Stop issuing new rules Week ahead: AT&T-Time Warner merger under scrutiny MORE (R-Texas), Marco RubioMarco RubioSenate GOP to Obama: Stop issuing new rules Juan Williams: McConnell won big by blocking Obama The ignored question: What does the future Republican Party look like? MORE (R-Fla.) and Kelly AyotteKelly AyotteJuan Williams: McConnell won big by blocking Obama Battle brews over Trump’s foreign policy Battle for the Senate: Top of ticket dominates MORE (R-N.H.), as well as prominent Democrats including Sens. Charles SchumerCharles SchumerDems press Trump to support ‘Buy America’ provision in water bill Overnight Finance: Trump takes victory lap at Carrier plant | House passes 'too big to fail' revamp | Trump econ team takes shape Anti-Defamation League: Ellison's past remarks about Israel 'disqualifying' MORE (N.Y.), Kirsten GillibrandKirsten GillibrandGOP chairman: Spending bill expected to last through April Vet groups applaud Trump's Defense pick of Mattis Dem lawmaker won't support waiver allowing Mattis to serve as defense secretary MORE (N.Y.) and Barbara MikulskiBarbara MikulskiThis Week in Cybersecurity: Dems press for information on Russian hacks Overnight Cybersecurity: Last-ditch effort to stop expanded hacking powers fails Intel Dems push for info on Russia and election be declassified MORE (Md.).

Lawmakers called on President Obama to "bring a renewed sense of urgency to the process.”

"Iran needs to understand that the time for diplomacy is nearing its end," they said. 

The letter comes as Hassan Rouhani was sworn in as Iran’s new president over the weekend. The White House on Sunday said the U.S. was willing to work with Iran, if the new leader engaged “substantively and seriously” on nuclear issues.

Congress, though, is working to enact tougher sanctions, with the House approving legislation last week to tighten controls against Iran's energy, shipping and insurance sectors.

Schumer last week said military action against Iran should never be taken off the table, but backed tightening sanctions as the preferred method to stop the country’s nuclear development.

“Ratcheting up the economic pressure against Iran is imperative,” he said last Wednesday on the Senate floor, “so that Iran sees it’s not in their best interests economically to continue on this path.”

The Pentagon has already drafted up plans for possible military action against Tehran, should the administration's strategy fail to stop Iran's nuclear program. 

However, Defense Department leaders continue to back the White House's approach of diplomatic and economic pressure to bring Tehran to heel. 

Iran’s regime insists its nuclear enrichment efforts are geared toward energy development, and not weaponization. 

Washington and its allies argue the Iranian program clearly puts the country on the path to developing nuclear arms.