Liberia has closed its border with Ivory Coast, after gunmen allegedly crossed into Ivory Coast and killed seven United Nations peacekeepers.

Information minister Lewis Brown announced the move during a news conference in Monrovia on Monday.

He said Liberia also has sent troops and police to protect the border area, and suspended mining activities in the region. Liberian authorities are still investigating where the gunmen were based.

Ivorian officials said Liberia-based gunmen killed seven U.N. peacekeepers and eight civilians on Friday in the western town of Tai, near the two countries' border.

U.N. peacekeeping chief Herve Ladsous, who will travel to Ivory Coast this week for a memorial service, briefed the U.N. Security Council Monday. Ladsous told reporters the United Nations still does not know who carried out the attack.

Before last week's shootings, Human Rights Watch had reported that mercenaries and militias based in eastern Liberia were carrying out cross-border raids and recruiting child soldiers. HRW accused Liberia of failing to hold the gunmen accountable.

The rights group said the attackers include Liberian mercenaries and Ivorian militiamen who fought for Ivory Coast's former president Laurent Gbagbo.

Mr. Gbagbo lost a 2010 presidential poll to President Alassane Ouattara but fought to remain in power. About 3,000 people were killed in a bloody power struggle between the two sides, until the former president was captured in April of last year. He has been charged with crimes against humanity and is being held in The Hague by the International Criminal Court.