Washington (CNN) President Donald Trump is facing new pressure to investigate the di sappearance of Saudi journalist Jamal Khashoggi and determine whether to impose sanctions on those responsible after receiving a letter from a bipartisan group of senators Wednesday.

The letter, which triggers an "investigation and Global Magnitsky sanctions determination" was penned by the top Republican and Democrat on the Senate Foreign Relations Committee, chairman Sen. Bob Corker and ranking member Sen. Bob Menendez, along with the leaders of the appropriations subcommittee for the State Department, Sen. Lindsey Graham and Democrat Sen. Patrick Leahy.

Under the terms of the Magnitsky legislation, the President can impose sanctions on individuals or countries that are deemed to have committed a human rights violation.

Trump said Wednesday night in an interview on Fox News that "so far it's looking a little bit like" the Saudis are behind the disappearance of Khashoggi, but said "I do hate to commit to what recourse we would take. It's too early."

The President said blocking further arms sales to Saudi Arabia "would be hurting us."

Trump said the US is doing well economically in part due to "what we are doing with our defense systems," and said, "frankly I think that would be a very, very tough pill to swallow for our country."

15-man team

Khashoggi, a former Saudi royal insider who became a critic of the regime of Crown Prince Mohammed bin Salman, has not been seen since Tuesday last week, when walked into the consulate general in Istanbul, intending to get paperwork that would allow him to marry his Turkish fiancée.

Turkish authorities have privately said they believe Khashoggi, a Washington Post columnist, was killed inside the consulate. The Saudis deny the allegation but have not been able to provide proof that he left the consulate alive.

In the latest developments on Wednesday, Turkish security officials concluded that the "highest levels of the royal court" in Saudi Arabia ordered the assassination of Khashoggi, according to a senior official cited by The New York Times.

Turkish officials have said that a 15-person team flew from Saudi Arabia into Istanbul on the day Khashoggi entered the consulate, and they have provided information about two private planes that, they say, were involved in the transit of these Saudis. Aviation data analyzed by CNN backs up evidence of the planes' arrival in Istanbul.

Trump said Wednesday that he's been in touch with the "highest levels" of the Saudi government about Khashoggi's case and expressed concerns about his possible murder. He said his administration was pressing the Saudi government to reveal more about the incident.

"We're demanding everything. We want to see what's going on here. It's a bad situation," Trump said in the Oval Office.

But he stopped short of saying whether he believed the Saudis have knowledge about his whereabouts, or may have played a role in his disappearance, stating that not enough was known to make a determination.

Senators' letter

The letter sent to Trump by the bipartisan group of senators increases the pressure on the administration to act. It gives the White House 120 days to "determine whether a foreign person is responsible for an extrajudicial killing, torture, or other gross violation of internationally recognized human rights against an individual exercising freedom of expression" and to report back to the Foreign Relations Committee with a decision on how it plans to act.

It specifically asks the President to make a determination in relation to Khashoggi.

Prior to the letter's release, senators were given access to a two-page classified report on Khashoggi, according to a Senate aide. "The intelligence reports are very direct, very short and give further credence to the fact that the focus needs to be on Saudi Arabia right now," Corker said.

Members of the Gang of Eight are being briefed in more detail: House Intelligence ranking Democrat Rep. Adam Schiff said he had been briefed on the matter, and Senate Intelligence ranking Democrat Mark Warner said he expected a briefing later.

One-fifth of the Senate — all members of the Senate Foreign Relations Committee besides Sen. Rand Paul — signed the letter.

"The entire Senate Foreign Relations Committee, sans Rand Paul, and the relevant appropriators all agreed to sign this request. The administration would be foolish not to follow the law here by rejecting their request," one Senate aide told CNN.

Asked if the letter puts pressure on the Trump administration, Corker responded, "Oh it does, of course."

"It's not intended though as a shot at them, it's intended to put in place ... it's the forcing mechanism to ensure that we use all the resources available to get the bottom of this and if in fact at the very highest levels of Saudi Arabia they have been involved in doing this, that appropriate steps will be taken to sanction them," Corker added.

Following the letter's release, Corker specifically noted that the sanctions could affect the highest levels of the Saudi regime.

"It's a very strong signal I think from the foreign relations committee. Again it's an act that we can take without passing legislation. It is a forcing mechanism. I don't look at this in any way to try to cross the bows of the administration. I don't. I do look at it certainly has a shot across the bow at Saudi Arabia and these are very serious steps," he said.

Corker also said that the administration was not given a heads up about the letter prior to its release to reporters, adding that he was unsure about how Trump might respond given his close relationship with the Saudi crown prince.

"This is a step that we are taking that we can take unilaterally that is a forcing mechanism and it does mean that in a serious way an investigation has to take place. And if in fact at the highest levels they have been involved in the murder of a journalist who just happened to write against some of the things they are doing in their country, they will be under tremendous pressure to follow this wherever it goes," he said.

The letter was also signed by Sens. Marco Rubio (R-Fla.), Ben Cardin (D-Md.), John Barrasso (R-Wyo.), Chris Murphy (D-Conn.), Jeff Flake (R-Ariz.), Tim Kaine (D-Va.), Cory Gardner (R-Colo.), Ed Markey (D-Mass.), Johnny Isakson (R-Ga.), Jeff Merkley (D-Ore.), Todd Young (R-Ind.), Jeanne Shaheen (D-NH), Rob Portman (R-Ohio), Cory Booker (D-NJ), Ron Johnson (R-Wis.), Chris Coons (D-Del.), Jim Risch (R-Idaho) and Tom Udall (D-N.M).