The United States told Israel that the extended Iran ceasefire will expire on Sunday, the Israeli public broadcaster KAN reported Wednesday.
Israeli sources said a breakthrough by that date "appears unlikely" and described what they called "confusion" in U.S. conduct.
U.S. Central Command (CENTCOM) separately announced that 31 vessels had been turned back under the naval blockade of Iranian ports, up from 29 reported earlier.
KAN said U.S. officials had conveyed to Tel Aviv that the timeframe Trump set for Tehran would end within days, citing an unnamed diplomatic source.
The broadcaster said Trump was seeking "understandings with Iran rather than open-ended negotiations."
Israeli sources told KAN that a breakthrough by Sunday appeared unlikely. They also described "confusion" in U.S. conduct, saying they had recently been learning about Trump's moves through media reports and his social media posts, an unusual admission of reduced coordination with Washington from one of its closest regional partners.
A White House official separately told Fox News on Wednesday that the ceasefire could last between three and five days. An Israeli source told KAN the situation remained unclear and depended "largely on Trump's decisions."
On Tuesday, Trump announced the ceasefire extension following a request from Pakistan, conditioning it on Iran presenting what he called a "unified proposal."
CENTCOM confirmed that 31 vessels had been directed to turn around or return to port under the naval blockade of Iranian ports, revised upward from 29 reported earlier Wednesday.
The blockade was launched on April 13, following weeks of disruption to shipping in the Strait of Hormuz since the war began on February 28.
CENTCOM also pushed back against media reports claiming that commercial ships had successfully evaded the blockade, calling the reports inaccurate.
The vessels M/V Hero II and M/V Hedy, reported to have slipped through, were in fact anchored at Chabahar, Iran, after being intercepted by U.S. forces earlier in the week.
The M/V Dorena remained under escort by a U.S. Navy destroyer in the Indian Ocean following a prior breach attempt.
Iran did not immediately respond to CENTCOM's characterization.