British Prime Minister Theresa May was to join Gulf Arab leaders at a summit in Bahrain on Tuesday for talks on trade after Britain's exit from the European Union.

Defence ties are also expected to figure high on the agenda as Britain builds a new naval base in Bahrain, while advocacy groups have urged May to raise human rights concerns.

She is the first British premier and the first woman to attend the annual summit of the six oil-rich Gulf Cooperation Council (GCC) states.

May's two-day visit comes as her government faces mounting domestic criticism that it has not done enough to avoid post-Brexit disruption to British trade, which is currently carried out under EU agreements.

"I will have the opportunity to talk to all six leaders about how we can develop our trade relationship, as well as cooperation on security and defence," May said before her arrival in Manama late on Monday.

Her office said May will discuss the possibilities for post-Brexit free trade arrangements with the GCC states -- Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates.

"As the UK leaves the EU, we should seize the opportunity to forge a new trade arrangement between the UK and the Gulf," the prime minister said.

Ahead of the summit opening later on Tuesday, May held talks with Bahraini officials that also focused on defence ties, the kingdom's official BNA news agency reported.

In October last year, Britain began building a naval base at Mina Salman, outside Manama, its first new permanent base in the Middle East in four decades.

May later told 300 Royal Navy officers aboard HMS Ocean that she wanted to "step up our defence and security cooperation to keep British citizens safe at home and abroad".

Britain's force already stationed in Bahrain was "a clear demonstration of the UK's enduring security commitment to the Gulf", she said.

- Criticism from rights groups -

Western ties with Bahrain, however, have come under criticism from international human rights groups.

Bahrain's Sunni minority rulers have cracked down on dissent since they crushed 2011 protests led by the Shiite majority for a constitutional monarchy with an elected prime minister.

The main Shiite opposition group, Al-Wefaq, once the largest in parliament, has been dissolved and scores of Shiites have been stripped of their Bahraini citizenship.

Amnesty International said Monday that the summit gave May a "unique opportunity to raise concerns over a pattern of recurring human rights violations throughout the region".

"In recent years across the Gulf we have seen human rights activists, peaceful political opponents and government critics systematically targeted in the name of security," said Randa Habib, the London-based watchdog's Middle East and North Africa director.

"It is high time for allies of the GCC to stop putting business and security cooperation before human rights, and Theresa May must not squander this opportunity to raise key rights issues," she added.