Iran has stepped up its harassment of U.S. Navy ships in the Persian Gulf, angering the U.S. military and members of Congress.

Since the international nuclear deal with Iran was implemented in early January, the number of incidents involving U.S. and Iranian ships in the Gulf has approximately doubled.

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The Navy has counted at least 31 interactions with Iranian naval forces deemed “unsafe,” “unprofessional,” or both, according to a defense official.

That's about as many such interactions that occurred all of last year, according to statistics provided to Fox News.

And those are also only counting interactions that have met the criteria of “unsafe” or “unprofessional.”

Overall, there were more than 300 interactions between U.S. and Iranian forces last year.

That figure includes incidents in which Iranian vessels waited for and followed U.S. ships transiting in the Persian Gulf, or sailed by with their weapons uncovered, in addition to other incidents of muscle flexing considered routine.

Military officials say there is no question that the behavior is getting worse.

“We've seen an uptick in confrontations by Iranian vessels in the Arabian Gulf,” Army Gen. Joseph Votel, the top U.S. commander in the region, said on Aug. 30. U.S. military officials refer to the Persian Gulf as the Arabian Gulf.

Votel also issued a rare warning to Iranian forces: “Ultimately if they continue to test us we're going to respond and we're going to protect ourselves and our partners.”

The last confrontation occurred just last Sunday, when seven Iranian fast attack boats confronted a U.S. Navy coastal patrol boat in international waters in the Persian Gulf.

When one of the Iranian vessels stopped directly in the path and within about 100 yards of the USS Firebolt, the U.S. vessel had to swerve to avoid a collision, defense officials said.

The confrontations are fueling anger on Capitol Hill and providing new arguments for lawmakers to enact anti-Iran legislation.

Earlier this week, a group of Republican senators introduced legislation that would ban any further U.S. government payments to Iran from a Treasury Department fund, until Iran returned $1.7 billion the administration sent to Iran earlier this year to settle a dispute over an arms deal from the 1970s.

“Iran's harassment of a U.S. naval vessel is just the latest example of troubling and unsurprising behavior by the regime following the Obama administration's parade of serious policy blunders that have emboldened Tehran and invited increased belligerence,” said Sen. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (R-N.H.), one of the bill's sponsors, in a statement Thursday.

Ayotte, who faces a tough reelection contest this year, also expressed concern that the money would buy “additional Iranian ships to harass U.S. Navy vessels,” among other weapons.

“I am deeply troubled that this large infusion of U.S. taxpayer-funded cash into the defense coffers of the world’s worst state sponsor of terrorism is going to further embolden Iran and result in our troops and our allies confronting more lethal and better equipped adversaries and potential adversaries,” she said.

The administration has insisted that any money going to Iran as a result of the Iran nuclear deal is not going to Iran's military.

“What they've told us but also what we see, instead of going to the military, the money is being poured back into the economy because this is an economy that was suffering terribly,” Antony Blinken, U.S. deputy secretary of State, said Wednesday on CNN's “New Day."

However, Blinken also said he could not guarantee that none of the money reached Hezbollah and other terrorist allies.

“We can't say not one single dollar. But what we can say, based on what we've seen so far, is that virtually all of it is going into the economy, not into the military,” he said.

“The bottom line is this, this agreement that we've reached has made us safer. It's put far into the future the day when Iran could enough material for nuclear weapons,” he said.

U.S. officials say they can't divine Iran's intentions with the stepped up confrontations, but indicate the regime is directly behind them.

“What I see is this is principally the regime leadership trying to exert their influence and authority in the region,” Votel said.

Votel also said that “90 percent” of the unsafe, unprofessional activities come not from the “general Iranian navy,” but from the Iranian Quds Force, which experts say has close ties to the Iranian regime.

Experts also expect that the confrontations will get worse.

“During the final phases of the nuclear deal negotiations, they toned it down a bit just so they wouldn't throw the negotiations too far off track,” said the Institute for the Study of War's Chris Harmer.

“Now that the deal is done, my expectation is that the harassment is going to escalate and probably increase beyond anything that we've seen,” Harmer said.