US Assistant Secretary of State for Democracy, Human Rights and Labour Tom Malinowski made the comments on his Twitter feed a day after Bahrain's Foreign Ministry said he is not welcome in the strategic island nation, which has long hosted the US Navy's 5th Fleet.
Bahrain alleged he intervened in the country's domestic affairs by holding meetings with some groups at the expense of others. The order to leave came after he held talks with Bahrain's main Shiite opposition group, Al Wefaq.
In his Twitter comments, Malinowski said Bahrain's decision to expel him is "not about me but about undermining dialogue. Those committed to reconciliation should not be deterred."
Tiny Bahrain continues to face low-level unrest more than three years after a Shiite-dominated opposition movement inspired by the Arab Spring protests took to the streets to demand greater political rights from the Sunni monarchy.
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Bahrain moved to crush the uprising with the help of security forces from Saudi Arabia and other neighbouring Gulf Arab states.
Repeated rounds of talks between the government and members of the opposition have failed to significantly defuse the tensions. Some Shiite factions oppose the dialogue efforts altogether because they don't think they will lead to real change.
Bahraini officials could not be reached to comment Tuesday on Malinowski's comments.
Malinowski visited Bahrain to reaffirm and strengthen bilateral ties and support King Hamad bin Isa Al Khalifa's reform and reconciliation efforts, US State Department spokeswoman Jen Psaki said yesterday.
She said the said the US is "deeply concerned" by Bahrain's demand that he leave and said Bahrain's government "is well aware that US government officials routinely meet with all officially recognised political societies."