The United States has warned Iran over its alleged support for Shi'ite Huthi rebels in Yemen, saying it will not "stand by" and let Tehran destabilize the region.
The warning from Secretary of State John Kerry comes amid calls by Tehran for peace talks to resolve the crisis in Yemen.
Speaking to the U.S. television station PBS on April 8, Kerry said Washington knows Iran is aiding the rebels in Yemen.
"There are obviously supplies that have been coming from Iran," he said. "There are a number of flights every single week that have been flying in."
Kerry added that the United States would back any state in the Middle East that felt threatened by Iran.
He said his country "is not going to stand by while the region is destabilized or while people engage in overt warfare across lines, international boundaries, and other countries."
The United States has stepped up its support for a Saudi-led coalition conducting air strikes and delivering weapons to Yemen's pro-government forces in their battle against Shi'ite Huthis and mutinous government forces.
The rebels have taken large parts of Yemen, including the capital, Sanaa.
Their drive into the key seaport of Aden forced President Abd-Rabbu Mansour Hadi to flee to Saudi Arabia.
Iran, which denies allegations it is providing military aid to the Huthi fighters, says it has dispatched a navy destroyer and another vessel to the Gulf of Aden.
Rear Admiral Habibollah Sayyari told state media on April 8 that the move aimed at "safeguarding naval routes for vessels in the region."
In a televised speech on April 9, Iran's Supreme Leader Ayatollah Ali Khamenei called for a halt in the two-week-old campaign of air strikes in Yemen, saying it was an act of "aggression" against Yemen and its people.
"This is a crime and genocide that can be prosecuted in international courts," he added.
Earlier on April 9, Iranian President Hassan Rohani said countries in the region should work to bring the country's rival factions to the negotiating table.
"A great nation like Yemen will not submit to bombing," he said. "Let us all think about ending war; let us think about a cease-fire."
On a visit to Pakistan, Iranian Foreign Minister Mohammad Javad Zarif met on April 9 with Pakistani Prime Minister Nawaz Sharif and Chief of Army Staff General Raheel Sharif.
The visit comes as Pakistan's parliament is debating whether to contribute forces to the Saudi-led coalition.
A Pakistani military statement said the talks between Zarif and Sharif focused on the situation in the Middle East, border management, and possible defense and security cooperation.
"The unity and integrity of the Ummah [the global community of Muslims] and greater harmony among the Muslims was emphasized," it added.
In Abu Dhabi, the foreign minister of the United Arab Emirates criticized Iran for "systematic" meddling in Yemen and said Tehran "is doing the same in Lebanon, Syria, Iraq, Afghanistan, and Pakistan."
Foreign Minister Sheikh Abdullah bin Zayed told a news conference on April 8 that Gulf Arabs could have "positive, normal" ties with Iran, but "each time we try to come close to Iran it starts spoiling the region."
Sheikh Abdullah also said any ground operation by the Saudi-led coalition would need a "green light" from what he called Hadi's "legitimate" Yemeni government.
In comments published on April 9, Turkish President Recep Tayyip Erdogan said Saudi Arabia, Turkey, and Iran "should be involved in efforts for a diplomatic solution" in Yemen.
In another development, Saudi Arabia's aviation authorities announced they prevented an Iranian plane carrying 260 pilgrims from entering the kingdom's airspace, saying the aircraft lacked appropriate permissions.
The pilgrims had hoped to arrive in Saudi Arabia on April 8 to perform Umrah, a pilgrimage to Mecca that can be undertaken at any time of year.
Fighting has intensified in the port city of Aden between the Huthis and militiamen loyal to the president, while coalition warplanes continued to bomb rebel targets across the country.
Amid a deteriorating humanitarian situation, boats carrying aid docked in Aden for the first time since the aerial campaign began on March 26.
The World Health Organization says at least 560 people were killed and some 1,700 others wounded in Yemen between March 19 and April 4.
Another 100,000 people fled their homes.