U.S. President Donald Trump said Thursday that the United States is under no pressure to end the war with Iran, but "the clock is ticking" for Tehran, as disruption from the conflict batters the world economy.

"I have all the time in the World, but Iran doesn't -- The clock is ticking!" Trump said on social media, adding that Iran's military was destroyed and "their leaders are no longer with us, the Blockade is airtight and strong and, from there, it only gets worse."

The USS George H.W. Bush aircraft carrier has arrived in the Middle East, the U.S. military said Thursday, bringing the number of the massive American warships operating in the region to three.

Air defense systems were activated in parts of Tehran on Thursday evening amid reports of hostile aerial activity, Iranian state media said in the first such reports since a ceasefire began.

The IRNA state news agency said the "sound of air defense firing" was heard in western Tehran, while the Mehr news agency reported that the systems were activated in several parts of the capital to counter "hostile targets", without elaborating further.

Israeli Defense Minister Israel Katz said on Thursday that Israel was "prepared to resume the war against Iran," adding that Israel was awaiting a green light from the United States to return Iran to "the Stone Age".

"The IDF (Israeli army) is ready both defensively and offensively, and the targets have been marked," Katz said in a video statement.

Tonight's second round of preparatory direct talks between Lebanon and Israel will be held at the White House instead of the State Department, Lebanese TV networks said.

The meeting is scheduled for 11:00 pm Beirut time (8:00 pm GMT).

An Israeli strike on southern Lebanon killed three people on Thursday, the Lebanese health ministry said, the latest attack despite a 10-day truce in the Israel-Hezbollah war.

In a statement, the ministry said that "an Israeli airstrike on the Shoukine road in the Nabatieh district," more than 30 kilometers (20 miles) north of Israel, killed three people while artillery shelling of the village of Yater wounded two people, including a child.

Lebanon's leaders accused Israel on Thursday of committing a war crime, after an airstrike killed a Lebanese journalist in the country's south, with the Israeli army saying it was reviewing the incident.

The Pentagon blasted as cherry picking and false on Thursday a news report saying that the department assessed it could take six months to completely clear the Strait of Hormuz of Iranian-laid mines.

The Washington Post reported on Wednesday that the Pentagon shared the six-month estimate during a classified briefing for the members of the House Armed Services Committee, citing three unidentified officials familiar with the discussion.

Britain and France Thursday voiced hope that a military plan to protect the Strait of Hormuz was coming together and would succeed in restoring trade flows through the vital passage.

The United Nations said Thursday it was "working on" maintaining a presence in Lebanon once the mandate for its UNIFIL peacekeeping force expires at the end of the year.

"In terms of the post-UNIFIL, we're currently in the process of working on these options," said Jean-Pierre Lacroix, the U.N. Under-Secretary-General for Peace Operations, with the Lebanese government "very clear that they would want to keep a U.N. presence".