Iran said on Wednesday it would not reopen the Strait of Hormuz as long as the U.S. naval blockade remained in place, calling it a "blatant violation" of the ceasefire between the longtime foes.
Iran's Revolutionary Guards meanwhile said their naval forces had seized two container ships trying to cross the strategic strait.
Foreign ministry spokesman Esmaeil Baqaei said the Islamic republic was appreciative of Pakistan's efforts to end the Middle East war but did not comment on a ceasefire extension announced by the United States.
President Donald Trump had said on Tuesday he was extending the truce following a request by Pakistani mediators and to allow more time for peace talks.
"A complete ceasefire only has meaning if it is not violated through a naval blockade," Iranian parliament speaker Mohammad Bagher Ghalibaf said Wednesday.
"Reopening the Strait of Hormuz is not possible amid a blatant violation of the ceasefire."
Despite the latest series of attacks on maritime traffic in the Gulf, a second round of U.S.-Iran talks could take place within the next three days, the New York Post reported, citing Trump and unnamed Pakistani sources.
"It's possible!" Trump reportedly wrote to the Post in a text message when asked about the sources in Pakistan, who had told the newspaper that a second round could happen within two to three days' time.
Trump also claimed that Iran had halted alleged plans to execute eight women arrested over anti-government protests, after he urged Tehran to release them.
But Iran's judiciary described his remarks as "false news," saying the women hadn't faced the death penalty in the first place.
- Ships seized -
U.K.-based maritime security monitors confirmed that three commercial vessels had reported incidents involving gunboats in the Strait of Hormuz, the international gateway for the Gulf oil and gas industry which U.S. and Iranian forces are battling to control.
"The Islamic Revolutionary Guard Corps naval force this morning identified and stopped in the Strait of Hormuz two violating ships," the Guards said.
"The two offending ships ... were seized by the IRGC's naval forces and directed to the Iranian coast."
They identified one ship as the Panama-flagged container ship MSC Francesca and the Liberia-flagged Epaminondas. The tracking site Marine Traffic showed the last known positions of both vessels closer to the Iranian coast of the strait, northeast of Oman.
Earlier, the British maritime security monitor UKMTO said one container ship reported it was fired upon by a boat belonging to Iran's Revolutionary Guards 15 nautical miles northeast of Oman, causing damage to the bridge but no casualties.
- 'Stateless, sanctioned' -
Separately, a third ship was fired upon and stopped in the water eight nautical miles west of the Iranian coast, UKMTO said, without identifying the attackers.
British Security firm Vanguard Tech identified it as the Panama-flagged container ship Euphoria, which it said was "transiting outbound of the Strait of Hormuz".
The U.S. Navy is attempting to block vessels heading to and from Iranian ports, while Tehran has said vessels must seek permission to leave or enter the Gulf through the strait, a conduit for a fifth of the world's oil and liquefied natural gas in peacetime.
The War Department said Tuesday that U.S. forces had intercepted and boarded a "stateless sanctioned" vessel. AFP has identified the ship as one linked to Iranian activity. Both sides accuse the other of ceasefire breaches.
Iran has all but shut the strait in the seven weeks since the United States and Israel launched a massive attack on the Islamic republic that plunged the Middle East into war.
- Lebanon front -
The fate of peace talks hosted by Pakistan remains unclear. A previous round collapsed with Tehran accusing the United States of making excessive demands over the Hormuz strait and its nuclear programme.
In Lebanon, which was dragged into war when Hezbollah launched rockets at Israel to avenge its killing of Iran's supreme leader, Israeli strikes killed four people on Wednesday, Lebanese state media said.
France's President Emmanuel Macron announced that a second French soldier, wounded in a weekend ambush against U.N. peacekeepers in Lebanon linked to Hezbollah, had died.
A first soldier was shot dead in the Saturday ambush, for which Hezbollah has denied responsibility.
The Lebanese daily newspaper Al-Akhbar said an Israeli airstrike wounded two of its journalists on Wednesday while they were working near the border with Israel.
A separate 10-day ceasefire was agreed between Israel and Lebanon on Friday and included Hezbollah.
Israel and Lebanon, which have no diplomatic relations, will hold fresh talks in Washington on Thursday, a State Department official told AFP.
Israeli attacks on Lebanon have killed at least 2,454 people since the start of the war, a Lebanese government body said in its latest toll.