There should be "no doubt" that the White House is willing to move forward unilaterally on immigration reform, President Obama said Thursday amid bipartisan calls for him to avoid acting alone.

"It continues to be my belief that, if I can't see the congressional action, that I need to do at least what I can in order to make the system work better," Obama told reporters at a news conference.

The president said that his preference continued to be for lawmakers to act on a comprehensive fix, and that "hope springs eternal" for Congress to take up the issue after the midterm elections. But in the meantime, Obama said the administration is plowing ahead with proposals for executive action.

"Have no doubt: in the absence of congressional action, I'm going to do what I can to make sure the system works better," Obama said.

Earlier this week, Sen. Marco RubioMarco Antonio RubioOvernight Defense: Senate passes 0B defense bill | 3,000 US troops heading to Afghanistan | Two more Navy officials fired over ship collisions Senate passes 0B defense bill Trump bets base will stick with him on immigration MORE (R-Fla.), a member of the Gang of Six that developed the Senate's comprehensive reform bill, sent a letter to the president warning that an executive action would "close the door to any chance of making progress on immigration reform for the foreseeable future."

Some vulnerable Senate Democrats have also expressed concern about the president acting in lieu of Congress.

"This is an issue that I believe should be addressed legislatively, and not through executive order," Sen. Kay HaganKay HaganLinking repatriation to job creation Former Sen. Kay Hagan in ICU after being rushed to hospital GOP senator floats retiring over gridlock MORE (D-N.C.) told The Wall Street Journal.

Sen. Mark PryorMark PryorMedicaid rollback looms for GOP senators in 2020 Cotton pitches anti-Democrat message to SC delegation Ex-Sen. Kay Hagan joins lobby firm MORE (D-Ark.), in a statement, said although he was also frustrated by partisanship in Washington, "that doesn't give the president carte blanche authority to sidestep Congress when he doesn't get his way."

Obama dismissed suggestions that the administration should be focusing its energies on addressing the tens of thousands of migrant children who have crossed the southern border.

The president said the administration had worked "systematically" and "in a serious way" to shift resources to the border to deal with the influx. He also said he was encouraged that it appeared fewer minors are now crossing the border.

"It would have been helped along if Congress had voted for the supplemental that I asked for. They did not. That means that we've got to make some administrative choices and executive choices about, for example, getting more immigration judges down there. So that has kept us busy," the president said.

"But it has not stopped the process of looking more broadly about how do we get a smart immigration system in place while we're waiting for Congress to act."  

— This story was updated at 6:55 p.m.