By Phuong Nguyen and Francesco Guarascio

HANOI, July 24 (Reuters) - Vietnam's police ministry has agreed to buy two Lockheed Martin helicopters, according to three people with knowledge of the talks, in what would be a key security deal since Washington lifted an arms embargo on the Communist-run nation a decade ago.

The deal would come after the country's ministry of public security held protracted talks since at least 2022 with multiple U.S. defence companies to acquire helicopters. Lockheed Martin LMT.N is also negotiating with Vietnam's defence ministry the sale of C-130 military transport planes, multiple officials have said.

The Southeast Asian country, which relies heavily on Russian weapons, has been looking for years to diversify its arsenal. It is also currently negotiating with the Trump administration key elements of a tariff deal that is crucial to maintain access to its largest export market.

Vietnamese pilots have already been training with Lockheed Martin's Sikorsky helicopters, one of the sources with direct knowledge said, noting the deal was worth more than $100 million and could include more choppers at a later stage.

The source did not specify the chopper model under discussion but said pilots were training with S-92 helicopters, which are employed in several countries for both civilian and military uses.

Another two sources briefed on the talks confirmed Vietnam had agreed to buy two Lockheed Martin helicopters but gave no information about the cost and the model.

All sources declined to be named because the information was not public.

Reuters could not establish when the deal could be completed and whether there were contractual aspects to be defined.

Since an arms embargo on Vietnam was lifted in 2016, U.S. security deals with its former foe have been limited to coastguard ships and trainer aircraft, which could lead to the procurement of military planes.

Lockheed Martin said queries on procurement should be directed to the Vietnamese government.

Calls to Vietnam's ministry of public security went unanswered. The foreign ministry did not reply to a request for comment.

Vietnam's parliament approved in June 2022 the establishment of a mobile police unit to tackle crime, terrorism and riots, which would need helicopters to operate, according to the government and the text of the 2022 legislation.

U.S. officials have said Washington sees Vietnam as a key player on regional security and would be willing to boost Vietnam's defence, especially in the South China Sea, where it is often at odds with China over disputed boundaries.

Support for the police could be more controversial. The latest U.S. State Department's report on human rights in Vietnam, released in 2023, warned of significant violations and abuses by security forces.

Vietnam's foreign ministry has said the report was biased and inaccurate.

The sources did not explicitly link the possible procurement deal to tariff talks, but Vietnamese and U.S. officials have repeatedly said purchases of U.S. military equipment would strengthen Hanoi's position in negotiating a fully-fledged trade agreement.

U.S. President Donald Trump announced earlier in July a deal on 20% tariffs for Vietnamese goods imported into the United States, 40% levies on transshipped products and no duties for U.S. exports to Vietnam.

However, Hanoi has instead talked of a preliminary framework agreement. Talks are still underway to finalise the agreement.

(Reporting by Phuong Nguyen, Francesco Guarascio and Khanh Vu; Editing by Shri Navaratnam)

((Francesco.Guarascio@thomsonreuters.com;))