The two-week ceasefire announced earlier this month will expire on April 22.
President Donald Trump announced "major combat operations" against Iran on Feb. 28, with massive joint U.S.-Israeli strikes targeting military, government and infrastructure sites.
Following the announcement of a two-week ceasefire, initial U.S.-Iran talks in Pakistan earlier this month failed to reach a peace deal. The original ceasefire is set to expire on April 22.
Trump said on Sunday that U.S. negotiators would return to Islamabad on Monday for a new round of talks. White House press secretary Karoline Leavitt said Vice President JD Vance would accompany special envoy Steve Witkoff and Jared Kushner, the president's son-in-law, to Islamabad.
But Iran's Foreign Ministry spokesperson said Monday that Tehran has "no plans" to participate.
At least 415 U.S. troops have been wounded in the war with Iran, according to Defense Department data.
Last week, the total stood at 399. The rise during the ceasefire is tied to delayed reporting of injuries, especially traumatic brain injuries, in which symptoms can emerge or be recognized days later.
-ABC News' Steven Beynon
As the Iran conflict drags on, President Donald Trump insists that he is not facing any time constraints to secure a deal, pushing back on reports that say he is under "pressure."
"I am under no pressure whatsoever, although, it will all happen, relatively quickly! Time is not my adversary," Trump wrote on social media.
The president insisted that he is ahead of schedule militarily.
"They like to say that I promised 6 weeks to defeat Iran, and actually, from the Military standpoint, it was far faster than that, but I'm not going to let them rush the United States into making a Deal that is not as good as it could have been," Trump wrote.
Vice President JD Vance is expected to leave for Pakistan on Tuesday for the next round of peace talks with Iran, according to two U.S. officials familiar with the plans. The sources cautioned that the situation is fluid and plans could change.
The State Department will host a second round of talks between Israel and Lebanon on Thursday, according to a State Department spokesperson.
"The United States welcomes the productive engagement that began on April 14," the spokesperson said. "We will continue to facilitate direct, good-faith discussions between the two governments."
