Ivory Coast and Liberia are to hold joint military exercises by the end of the year, the presidents of the two countries said on Thursday, noting that joint action has helped to curb attacks in western Ivory Coast by armed groups based in eastern Liberia.

During a three-hour meeting in Abidjan, Liberian President Ellen Johnson Sirleaf and her Ivorian counterpart Alassane Ouattara decided on "joint military and security manoeuvres by the end of 2012," according to a statement issued following the talks.

Since the end of the 2010-2011 crisis in Ivory Coast, which left 3,000 dead in the wake of a disputed presidential election, western Ivory Coast has been targeted by raids carried out by armed groups based in eastern Liberia.

Ouattara's government says the groups are made up of exiled backers of former president Laurent Gbagbo, Ouattara's rival in the 2010 election. Gbagbo's party denies any link to the attacks.

On Thursday, Sirleaf, who was on a one-day visit in Ivory Coast, and Ouattara noted that steps taken by the two countries in recent months had made it possible to "greatly reduce tensions on the border."

They also announced "a major meeting between politicians and traditional chiefs of the communities living on the two sides of the border" at an unspecified date.

"The security situation in our country has improved, in part thanks to you, thanks to your efforts," Ouattara told Sirleaf.

The security forces of the two countries had worked together "very well" in monitoring the border and fully cooperated in the face of threats to "peace and stability", Sirleaf said, adding that the cooperation would continue.

The statement also noted that the two countries had managed to cut the number of Ivorians who had taken refuge in Liberia from 145,000 at the height of the crisis to "fewer than 60,000 today".

The Liberian government said Thursday it had arrested the mastermind of one cross-border attack, a Liberian national named Bobby Shappy Julu. He is accused of orchestrating an ambush in southwest Ivory Coast on June 18 in which 18 people died, including seven United Nations peacekeepers from Niger.

On July 17 Liberia announced the arrest of three people linked to the attacks. Two others gave themselves up and another was arrested in September.

Last month the United Nations Security Council called on Liberia and Ivory Coast to work more closely together in monitoring their joint frontier.

A recent report by UN experts backed up charges by Ivory Coast that attacks on its security forces, particularly in Abidjan, since August were the work of pro-Gbagbo exiles in Ghana, working with armed militants based in Liberia. They deny the charge.