President Biden on Thursday will announce an end to U.S. support for offensive operations in Yemen, where a brutal civil war has resulted in one of the world's worst humanitarian crises, White House national security adviser Jake Sullivan said at a press briefing.

Why it matters: Pulling support for the war in Yemen was one of Biden's top foreign policy campaign promises. It marks a significant reversal from U.S. policy under former President Trump, who vetoed bipartisan resolutions passed by Congress that called for the U.S. to stop providing weapons to the Saudi-led coalition in Yemen.

Between the lines: It's unclear what kinds of support the Biden administration will continue to provide to Saudi Arabia, a U.S. ally that led the 2015 intervention in Yemen against the Iran-backed Houthi rebels that toppled the pro-Saudi government in Sana'a.

• Sullivan said Thursday that the halt in support will include suspending two arms sales of precision-guided munitions that had been signed off on by the Trump administration.
• He added that the suspension does not apply to U.S. actions against Al-Qaeda in the Arabian Peninsula, and that Biden would announce a special envoy for Yemen later on Thursday as part of a strategy to play a "more active, engaged role in diplomacy to bring an end to the conflict."

What they're saying: "We have spoken with both senior officials in the UAE and senior officials in Saudi Arabia," Sullivan said. "We have consulted with them. We are pursuing a policy of no surprises when it comes to these types of actions so they understand that this is happening and they understand our reasoning and rationale for it."