Deputy Foreign Minister Xalaf Xalafov met Ambassador Irfan Siddiq on July 1 and strongly protested against the visit, the ministry said in a statement.

Bako Sahakyan, leader of Azerbaijan’s separatist region of Nagorno-Karabakh, is scheduled to deliver a speech at Chatham House on July 8.

The visit isn’t in keeping with the spirit of the "friendly ties and strategic relationship” between Azerbaijan and the UK, Xalafov said in the statement. It will be a move against Azerbaijan’s sovereignty and territorial, he said.

The British embassy said in a statement that the UK does not recognize the "self-proclaimed Nagorno Karabakh republic” and has no contact with any of its representatives.

Sahakyan is traveling to the U.K. "independently”, the embassy said, adding that the British government has no role in the visit.

The embassy also said the Chatham House is an independent institution, which makes its own decisions about who to invite to its events.

Armenians captured nearly one-fifth of Azerbaijan’s internationally recognized territory, including Nagorno-Karabakh and seven adjacent districts, in a war in the early 1990s, expelling the entire Azerbaijani population (as many as 700,000).

While major hostilities ended with a ceasefire in 1994, no peace agreement has been signed.

British energy giant BP has major stakes in Azerbaijan’s largest oil and natural gas projects – ACG and Shah Deniz. The company operates both projects and also the Baku-Tbilisi-Ceyhan main export pipeline.