Marco Rubio took sharp aim at Ted Cruz over national security Monday night, accusing his Republican presidential rival of voting to "weaken" surveillance efforts as he warned that deadly attacks like those just carried out in Paris could happen in the United States.

The comments, which his campaign quickly pushed on social media, signaled that Rubio is eager to press the issue against his Senate colleague, with whom he has clashed mostly over immigration so far.

"We are vulnerable. What happened in Paris could happen in a major American city at any moment, at any time," said Rubio. Threats to the homeland make United States intelligence gathering crucial, he added, before name-checking his Texas colleague.

"I think it's a distinctive issue of debate in the presidential race. At least two of my colleagues in the Senate aspiring to the presidency, Senator Cruz in particular, have voted to weaken the U.S. intelligence programs, just in the last month and a half," said Rubio. "And the weakening of our intelligence gathering capabilities leaves America vulnerable."

Rubio, a Florida senator, made his remarks during a moderated discussion at the Wall Street Journal CEO Council annual meeting in Washington. Later in the talk, he went after Cruz on immigration, an issue the two have clashed over in recent days.

But the remarks on surveillance, coming at a time of intensifying scrutiny on national security, were most notable. Rubio aides posted video of his remarks online and sought to spread it widely on social media. Jim Merrill, Rubio's top New Hampshire hand tweeted the hashtag "#phonytedcruz" along with a link to the video.

Rubio's campaign pointed to Cruz's support for the USA Freedom Act of 2015, among other things. The bill passed the Senate in June and was signed by President Obama.

The legislation banned the bulk collection of data of Americans’ telephone records and Internet metadata and it limited the government’s data collection to the “greatest extent reasonably practical." Cruz was one of 67 senators who voted for final passage while Rubio was one of 32 who voted against it.

Cruz spokesman Rick Tyler, asked to respond to Rubio's remarks, said: "Does Senator Rubio think Senators Scott, Ayotte, and Grassley also 'voted to weaken the U.S. intelligence programs.'?"

The Republican senators Tyler named represent the first three states in the Republican nominating contest.

During the fourth presidential debate last week, Rubio argued with Sen. Rand Paul (R-Ky.), a much more dovish Republican whose rise in national politics is due in large part to his well-documented complaints about National Security Agency surveillance techniques. Cruz jumped in, positioning himself as an ideal "middle ground" between his two opponents.

On Syria, Rubio called Obama’s decision to send 50 special operations advisers into the country "insufficient," Monday, but he declined to say how many would be enough.

"Ultimately, the numbers need to be set by the tacticians," he said.