Top Senate Democrats are warning they could block a bipartisan Iran sanctions bill if it does not include tougher financial penalties on Moscow.

Sen. Ben Cardin Benjamin (Ben) Louis CardinPelosi hopeful COVID-19 relief talks resume 'soon' Congress must finish work on popular conservation bill before time runs out PPP application window closes after coronavirus talks deadlock MORE, the top Democrat on the Foreign Relations Committee, will not agree to move the Iran bill to move forward on the floor "until there is a clear and satisfactory path forward on Russia sanctions," a senior aide to the Maryland Democrat said Thursday.

The Cardin-McCain bill would would slap financial penalties on Russia for its election interference, as well as ongoing conflicts in Ukraine and Syria. It would codify sanctions implemented under the Obama administration by executive order.

Most Republicans have held off from backing new Russia sanctions as they tried to give the Trump administration time to improve the U.S.-Russia relationship, which soured under the Obama administration, and make progress in Syria.

But top Republicans are appearing increasingly confident this week that they will pass new penalties against Russia, even amid investigations into potential contacts between President Trump’s campaign and the Russian hackers who meddled in the presidential election.

The senior aide for Cardin downplayed the chances that a Russia proposal wouldn't be included, but added the Maryland Democrat wants to make sure what ends up in the Iran bill is "as strong as possible."

"Lots of proposals circulating and some have seemed unsatisfactory to him," the aide said.