Updated

Senators have dropped a demand for a public declaration of how many civilians the United States kills in CIA drone strikes each year after the U.S. intelligence chief expressed concerns, congressional aides said.

The provision was included in Congress' main intelligence bill for 2014, which passed a committee vote in November but hasn't been adopted by the full Senate yet.

President Obama tightened rules for drone attacks last year, partly to limit unintended casualties, and deaths have declined significantly since then. U.S. officials say few civilians have died from drone attacks in Pakistan, Yemen and elsewhere over the last decade, though unofficial tallies by human rights groups cite higher figures.

The government doesn't release casualty figures for drone strikes.

The New America Foundation, for example, maintains a database of the strikes using reports in major news media that rely on local officials and eyewitness accounts. It says at least 339 civilians died in Pakistan and Yemen, most after Obama became president in 2009. It labels a similar amount of the dead as "unknown" — neither militants nor noncombatants.

Pakistan's government told the U.N. last year the approximately 2,200 people killed by drone strikes included at least 400 civilians.

Aides said the reporting requirement has now been eliminated from the Senate bill. They spoke on condition of anonymity because they weren't authorized to speak publicly on the matter. It's unclear when the legislation may be sent to the Senate for a vote on its passage.

"The executive branch is currently exploring ways in which it can provide the American people more information about the United States' use of force outside areas of active hostilities," Director of National Intelligence James Clapper wrote in a letter April 18 to Dianne Feinstein, D-Calif., the Senate Intelligence Committee chairman.

He expressed reservations with the bill's requirements, however.

"To be meaningful to the public, any report including the information described above would require context and be drafted carefully so as to protect against the disclosure of intelligence sources and methods or other classified information," Clapper said.

"We are confident that we can find a reporting structure that provides the American people additional information to inform their understanding of important government operations to protect our nation, while preserving the ability to continue those operations."

Rights activists decried the change.

"When it comes to killing people, the administration's 'trust us' approach simply isn't good enough," said Zeke Johnson, director of Amnesty International USA's security and human rights program.

"Congress should be conducting vigorous oversight," he said. "Years after Obama's first strike, we're still in the dark about basic information, including the number of people killed, their names, and the legal memos used to justify the killings."

A House bill would still compel Obama to do some of those things, though its support is uncertain.

The legislation proposed by Reps. Adam Schiff, D-Calif., and Walter Jones, R-N.C., would require Obama to produce an annual report with numbers of militants and civilians killed everywhere except in Afghanistan. The administration also would have to provide figures dating back to 2009. Because the CIA drone program is covert, some have balked at public reporting requirements.

Obama gave a speech announcing an overhaul of his drone policy in May 2013. Now, strikes only target high-level terrorist targets that can't otherwise be captured, and when there is near certainty of no civilian casualties. U.S. drone attacks have dropped dramatically in recent months, especially in Pakistan.

Last week, Yemen's military, reportedly backed by U.S. drone strikes, hit a major Al Qaeda base in southern Yemen and killed 55 people, including militants. A day earlier, a U.S. drone strike in southern Yemen killed at least nine suspected Al Qaeda militants and three civilians, Yemeni authorities said.