DUBAI- Qatar’s sovereign wealth fund has not been liquidating foreign assets to support the Gulf state's banking system since other Arab countries imposed an embargo on Qatar last June, according to the fund's chief executive.

The embargo caused heavy outflows of deposits from Qatari banks in the initial months, and central bank data shows government bodies protected the banks by depositing about $30 billion in them between June and December.

Outflows have now essentially ceased, removing the need for a government support operation, but bankers said much or most of the emergency deposits in banks last year came from the QIA.

However, Sheikh Abdullah bin Mohamed bin Saud al-Thani, who runs the Qatar Investment Authority (QIA), said the fund, with assets unofficially estimated at about $300 billion, did not need to sell foreign assets to raise cash, and indeed was about to announce "the deal of a lifetime".

"How can I liquidate assets -- as they speculate -- and at the same time I keep buying others," he was quoted as telling the Lusail newspaper.

"Two days ago, we signed a deal in Miami and we will announce it in the next few days," he added without elaborating.

Sheikh Abdullah said the QIA had a privileged position in global markets and would keep investing around the world.

He was speaking in the United States as he accompanied Qatari Emir Sheikh Tamim bin Hamad al-Thani, who visited President Donald Trump last week. Sheikh Tamim returned to Doha on Saturday.

The QIA's investments in the United States are stable and strong, and it has so far spent $35 billion executing about 60 percent of its U.S. investment plans for the period 2015-2020, Sheikh Abdullah added.

In recent months the QIA has, among other deals, reduced its stakes in upscale jeweller Tiffany & Co TIF.N and Swiss bank Credit Suisse .

A banker in the Gulf who does business with the QIA told Reuters he understood the disposals were due to portfolio adjustments and assets presenting attractive profit opportunities, rather than the result of any scramble to raise money for use within Qatar.

The QIA is looking for investment opportunities in the United States and Asia, the banker said.

(Reporting by Aziz El Yaakoubi; Additional reporting by Saeed Azhar and Dasha Afanasieva; Editing by Andrew Torchia and Kevin Liffey) ((aziz.elyaakoubi@thomsonreuters.com; +971552994086);))