Israel-Gaza updates: Israel says ground operation underway in southern Gaza

The Israeli Prime Minister's Office said Wednesday that 161 hostages are still being held in the Gaza Strip.

Of the 161 remaining hostages, 126 are male and 35 are female. Among them are 146 Israelis and 15 foreigners, including Americans. Ten of them are age 75 and older, four are 18 or 19, and four are under the age of 18, according to the Israeli Prime Minister's Office.

So far, 86 hostages -- 66 Israelis and 20 foreigners -- have been freed since last Friday in exchange for the release of dozens of Palestinians from Israeli prisons as part of a cease-fire agreement between Gaza's militant rulers, Hamas, and Israel. Another prisoner swap is expected to take place Wednesday.

-ABC News' Jordana Miller, Joe Simonetti and Morgan Winsor

The United States' Special Presidential Envoy for Hostage Affairs Roger Carstens, often referred to as the country's top hostage negotiator, will travel to Israel on Wednesday, according to a senior official in the U.S. Department of State.

The official said that Carstens "will support Secretary Blinken's visit to the region, meet with Israeli government counterparts and visit the families of Americans held hostage in Gaza."

U.S. Secretary of State Antony Blinken is expected to arrive in Israel on Wednesday night.

It will be Carstens' first known trip to Israel since Oct. 7, when Palestinian militant group Hamas carried out an unprecedented attack on southern Israel and took hundreds of people hostage back to the neighboring Gaza Strip. Carsten's deputy, Steven Gillen, visited Israel shortly after the war broke out and has spent a substantial amount time in the region during the weeks that followed, largely coordinating with Israeli officials on efforts to free the hostages.

Earlier this month, Carstens met with family members of some of the hostages in Washington, D.C.

-ABC News' Shannon Crawford and Morgan Winsor

White House National Security spokesperson John Kirby said there's no indication that Hamas is trying to keep Americans as hostages in order to use them as leverage.

"There's no indication that Hamas is trying to play some sort of game here in terms of the Americans," Kirby told reporters Tuesday.

He added that the first test case of getting hostages out involved two Americans, including a teenager from the Chicago area, and that 4-year-old American-Israeli hostage Abigail Idan was released over the weekend.

In the latest exchange on Tuesday, 12 hostages -- 10 Israelis and two foreign nationals from Thailand -- were released, the Israeli government said.

Kirby reiterated that the pool of American hostages is "pretty small, and the pool of Americans that qualify right now, women and children, is smaller still."

He also noted that there are issues locating the hostages, who may be held by various groups.

The U.S. believes there are eight or nine Americans still being held in Gaza, Kirby said on Monday.

-ABC News' Selina Wang and Cheyenne Haslett

Releasing more hostages will be a "prime" focus of Secretary of State Antony Blinken's latest trip to the Middle East, the White House said.

"We're up around 70 or so hostages out so far, which is good. It's a good start, but it's just a start. There are many more," White House National Security spokesperson John Kirby told reporters Tuesday. "We want to get them all back."

Blinken will also meet with his Israeli counterparts to reassure them of U.S. support and talk about getting humanitarian assistance to Gaza, Kirby said.

This week's trip will be Blinken's fourth to the region since the Oct. 7 attack.

-ABC News' Cheyenne Haslett