WASHINGTON (AP) — Israel warned U.S. Defense Secretary Lloyd Austin in a call Tuesday that a military operation was going to take place in Lebanon but gave no details, U.S. officials said Thursday. The same day of the call, in an attack widely blamed on Israel, thousands of pagers belonging to Hezbollah militants exploded.

The call was one of four between Austin and Israeli Defense Minister Yoav Gallant this week as attacks have spiked between Israel and Hezbollah, fueling worries that they could escalate into a wider regional war.

The two spoke again later Tuesday, and the U.S. has acknowledged being briefed following the attack. There was another call Wednesday, and they also spoke Sunday, said the officials, who spoke on condition of anonymity to discuss private talks.

The officials said the U.S. did not get advance warning of the second wave of attacks, with walkie-talkie radios targeted Wednesday. At least 37 people were killed, including two children, and some 3,000 wounded in the two days of explosions.

The officials stressed that the U.S. played no role in the attacks and said they were surprised by the specifics of the operations.

The attacks on electronic devices this week appeared to be the culmination of a monthslong operation by Israel to target as many Hezbollah members as possible all at once — but civilians were also hit.

Pentagon spokeswoman Sabrina Singh on Thursday acknowledged the four calls but did not provide timelines of when they happened. She said the U.S. has not made any changes in its force posture in the region as a result of the recent surge in attacks.

During a call Wednesday with Gallant, Austin spoke about regional security developments and reiterated America's unwavering support for Israel in the face of threats from Iran, Hezbollah and other Iranian proxies in the region, Singh said.

Austin "emphasized the U.S. commitment to deterring regional adversaries, deescalating tensions across the region, and reaffirmed the priority of reaching a cease-fire deal that would bring home hostages held by Hamas," she said.

He also pushed for a diplomatic solution that would allow civilians on both sides of Israel's northern border with Lebanon to return to their homes, Singh said.

Asked about the potential for a U.S. military evacuation of American citizens in Lebanon, Singh said the Pentagon has not gotten a request from the State Department to do that. State did urge U.S. citizens in Lebanon to maintain a low profile and review their security awareness in alerts this week.

State Department and White House officials say there are longstanding contingency plans for the potential evacuation of Americans in Lebanon but they have no information to suggest that those will become operational anytime soon.

"We have evacuation plans available for places all over the world," National Security Council spokesman John Kirby told reporters Wednesday. "But I wouldn't lead that to believe that we're in a moment now where we think we need to imminently call for that or act on that right now."

Other officials said U.S. Navy ships with Marines on board are already well-positioned in the Mediterranean Sea to assist if asked.

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AP Diplomatic Writer Matthew Lee contributed from Washington.