The head of Bahrain's largest Shia opposition movement will face prosecutors Thursday after police in the Sunni-ruled kingdom interrogated him over a meeting with a senior US diplomat.

Cleric Ali Salman, who heads Al-Wefaq, and his political assistant, former MP Khalil Marzooq, were summoned by police Wednesday to appear before the public prosecutor, the movement said.

That came after police questioned them the same day about the "meeting with US Assistant Secretary of State" Tom Malinowski and the "political situation in Bahrain and the region," said Al-Wefaq.

On Monday, Bahrain told Malinowski, who is the assistant secretary of state for democracy, human rights and labor, that he was "unwelcome" in kingdom and should "leave immediately."

The Gulf state's interior ministry confirmed that the two Shia leaders were questioned separately on Wednesday over the meeting with Malinowski.

Al-Wefaq said the move "accentuated the crisis" in Bahrain and demonstrated "the lack of willingness for dialogue" by the authorities to resolve the issue.

The ministry said the meeting at the US embassy violated a rule stipulating that contacts between political associations and foreign parties "should be coordinated with the foreign ministry and in the presence" of its representative.

The rule also stipulates that the justice ministry, which oversees political associations, should be informed of such meetings "at least three days in advance."

The interior ministry said the two opposition figures were allowed to leave after questioning, and that the public prosecutor would decide on any eventual action.

Al-Wefaq said on its Facebook page that Salman's lawyers were not allowed to attend Wednesday's questioning focused on the meetings with Malinowski.

The foreign ministry said Malinowski had met "with a particular party to the detriment of other interlocutors," describing his action as an "interference in its internal affairs."

Malinowski was the Washington director for Human Rights Watch, a vocal critic of Manama's crackdown on protests, until he took his current job in April.

Shia-led protests erupted in Bahrain in February 2011, taking their cue from uprisings elsewhere in the Arab world and demanding democratic reforms in the absolute monarchy.

Security forces boosted by Saudi-led troops crushed the protests a month later, but smaller demonstrations frequently take place in Shia villages, triggering clashes with police.

The foreign ministry said relations between Manama and Washington would not be affected by the "unfortunate acts" of Malinowski.

Bahrain is a strategic archipelago just across the Gulf from Iran. Washington is a long-standing ally of the ruling Al-Khalifa dynasty, and Bahrain is home to the US Navy's Fifth Fleet.