By Mohammad Yunus Yawar and Asif Shahzad

KABUL/ISLAMABAD, March 2 (Reuters) - Afghanistan and Pakistan said on Monday that their militaries had targeted each other's posts across the border as their fighting entered a fifth day, fuelling instability in a region rocked by U.S.–Israeli strikes on Iran and Tehran's retaliation.

The intensity of the clashes, however, appeared to be lower than when it began although there were no signs that the allies-turned-foes were seeking to step back and make peace.

UK Prime Minister Keir Starmer said Monday British military bases in Cyprus will not be used by the United States in its war with Iran, despite criticism from US President Donald Trump.

Starmer's government has been swept up in fallout from the spreading war in the Middle East.

On Sunday, Iranian-made drones hit a British base in Cyprus. Trump meanwhile slammed the UK leader's initial refusal to allow the use of British military facilities.

Starmer announced on Sunday he had agreed to a US request to use British bases for a "specific and limited defensive purpose".

WASHINGTON, March 2 (Reuters) - It will take time to achieve U.S. military objectives in Iran and additional U.S. casualties areexpected, U.S. General Dan Caine, the chairman of the Joint Chiefs of Staff, said on Monday.

The U.S.-Israeli air war against Iran expanded on Monday with no end in sight. The U.S. military said Kuwait's air defenses had mistakenly shot down three American F-15E fighter jets during an Iranian attack.

President Donald Trump warned Monday of a longer Iran war and refused to rule out ground troops, as his top diplomat suggested the timing of the US military operation was triggered by Israel.

Trump's brief remarks at the White House were his first in public since launching the strikes, after two Truth Social videos and a string of sometimes contradictory phone calls to media outlets.

Under relentless Israeli-US attack, Iran has bombarded US assets in the Gulf, but so far has not touched Turkey which would be a "high-cost strategic gamble" that could go disastrously wrong, analysts said.

Iran had long warned that if Washington attacked, it would target its regional assets -- which in principle should include NATO-member Turkey where US troops are stationed at several bases.

US President Donald Trump warned that his attack on Iran could run longer than a month, as Tehran retaliated to ongoing strikes by targeting US allies in the Gulf and drones hit the US embassy in Saudi Arabia on Tuesday.

Shortly after the United States urged Americans to flee all Middle Eastern nations from Egypt eastward, two drones hit the US embassy in Riyadh, sparking a quick vow by Trump to retaliate "soon", without elaborating how.

By Nidal al-Mughrabi and Pesha Magid

CAIRO/JERUSALEM, March 2 (Reuters) - Gaza is rapidly running out of its limited fuel supply and stocks of food staples may become tight, officials say, after Israel blocked the entry of fuel and goods into the war-shattered territory, citing fighting with Iran.

Israel's military closed all Gaza border crossings on Saturday after announcing air strikes on Iran carried out jointly with the United States. Israeli authorities say the crossings cannot be operated safely during war and have not said how long they would be shut.

By Ismet Mikailogullari

KAPIKOY, Turkey, March 2 (Reuters) - Hundreds of Iranians crossed the border into Turkey on Monday afternoon as the U.S.-Israeli war against Iran expanded, a Reuters witness said, with those arriving speaking of fear in Tehran and queues at petrol stations.

WASHINGTON, March 2 (Reuters) - U.S. Defense Secretary Pete Hegseth said on Monday that military operations against Iran would not lead to an "endless war" and that the aim was to destroy Tehran's missiles, Navy and other security infrastructure.

"We're hitting them surgically, overwhelmingly and unapologetically," Hegseth said during a press conference at the Pentagon.

(Reporting by Phil Stewart, Idrees Ali, Doina Chiacu; editing by Susan Heavey)

ASHGABAT, March 2 (Reuters) - Russia's embassy in Turkmenistan said on Monday that Russians unable to leave Iran could depart via Turkmenistan, a Central Asian former Soviet republic which shares a 1,148-kilometre (713-mile) border with northeastern Iran.

In a statement posted on Telegram, the embassy said Russians looking to leave via Turkmenistan could register with the Russian embassy in Tehran.