Paul Whelan's sister describes moment she met eyes with Russian Foreign Minister Sergey Lavrov

Elizabeth Whelan said she was "surprised" to meet the eyes of Russian Foreign Minister Sergey Lavrov during a meeting of the United Nations Security Council in New York City on Monday.

Elizabeth Whelan is the sister of Paul Whelan, a Canadian-born former U.S. Marine who has been detained in Russia for more than four years. She was invited to attend Monday's meeting, during which U.S. ambassador to the U.N. Linda Thomas-Greenfield accused Russia of violating international law by wrongfully detaining Americans and called for Paul Whelan's release. Lavrov chaired the meeting because Russia holds the U.N. Security Council's monthly rotating presidency for April.

"I was surprised he looked in my direction at all. I really expected him just to shuffle papers," Elizabeth Whelan told ABC News' George Stephanopoulos during an interview Tuesday on "Good Morning America."

"But I was really glad that he looked up and saw me standing there as the face of my brother," she added. "My brother is in a forced labor camp in a distant [Russian] province -- not somebody that Lavrov has to deal with at all. But to be there, a physical presence, reminding him about Paul's wrongful detention, I think it probably made the point."

Paul Whelan, a Michigan-based corporate security executive with U.S., British, Irish and Canadian citizenship, was visiting Moscow to attend a wedding in December 2018 when he was arrested on suspicion of espionage -- a charge both he and the U.S. government deny. He was convicted in 2020 and sentenced to 16 years in a Russian prison camp. He was left out of two separate prisoner exchanges between the United States and Russia last year.

"There are so many very good and intelligent people who are committed to getting Paul home, but we are always concerned," Elizabeth Whelan told ABC News. "Paul has been left behind twice, you know, that's just a fact. And it's really important that we stress that that cannot happen again. Paul Whelan must be part of any deal that happens in the future."

"But I do have faith that we are going to get him back," she added.

U.S. Secretary of State Antony Blinken has "put an offer on the table," according to Thomas-Greenfield.

"We are pushing the Russians to accept that offer and allow Paul to get back home to his family," Thomas-Greenfield told ABC News during Tuesday's interview. "Elizabeth said yesterday she doesn't know what her brother looks like. That was a powerful message for all of us to hear."

Elizabeth Whelan said the last time she spoke to her brother was in December 2018, "when he was telling us that he was going to go help this friend of his in Moscow and he was sorry that he wasn't going to be able to join us for Christmas." Since being detained in Russia, she said her brother has only been allowed to speak with their parents in brief telephone calls.

"I haven't seen a photo of him, I haven't heard his voice," she told ABC News. "We miss him terribly."

She said her brother spoke to their parents on Monday, revealing that he was able to watch the Russian broadcast of the U.N. Security Council meeting and saw his sister there.

"I don't know whether he heard any of our words or what we said," she added. "But the fact that he knows we're standing up for him, that we have not given up, that the United Nations has now heard about Paul Whelan, I think that's really important to him."

Thomas-Greenfield said Lavrov not only heard a "powerful message from me" but also "from the other 13 members of the Security Council" during Monday's meeting.

"I hope that he takes this message for what it was," she told ABC News. "And I hoped that he would look in Elizabeth's face and see what their actions are doing to a family member, and I think he did."

ABC News' Ariane Nalty and Jen Pereira contributed to this report.