Iranian missiles coming into Yemen through Oman?

Reuters:

Iran has stepped up weapons transfers to the Houthis, the militia fighting the Saudi-backed government in Yemen, U.S., Western and Iranian officials tell Reuters, a development that threatens to prolong and intensify the 19-month-old war.

The increased pace of transfers in recent months, which officials said include missiles and small arms, could exacerbate a security headache for the United States, which last week struck Houthi targets with cruise missiles in retaliation for failed missile attacks on a U.S. Navy destroyer.

Much of the recent smuggling activity has been through Oman, which neighbors Yemen, including via overland routes that take advantage of porous borders between the two countries, the officials said.

That raises a further quandary for Washington, which views the tiny Gulf state as a strategic interlocutor and ally in the conflict-ridden region. A senior U.S. administration official said that Washington had informed Oman of its concerns, without specifying when.

"We have been concerned about the recent flow of weapons from Iran into Yemen and have conveyed those concerns to those who maintain relations with the Houthis, including the Omani government," the official told Reuters.

Oman denies any weapons smuggling across its border, and its officials could not be reached for comment. Yemeni and senior regional officials say the Omanis are not actively involved with the transfers, but rather turning a blind eye and failing to aggressively crack down on the flow.
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The U.S. and Western officials who spoke to Reuters about the recent trend in arms transfers said it was based on intelligence they had seen but did not elaborate on its nature. They said the frequency of transfers on known overland smuggling routes had increased notably, though the scale of the shipments was unclear.
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It is the only logical route for Iran to get weapons into Yemen.  The Saudis' air campaign makes air resupply unlikely and the naval blockade by several of the Saudi allies stops Iran from delivering to Yemeni ports.  That leaves some clandestine efforts by Iran through the neighboring country of Oman.