Kenya sent an undisclosed number of troops into southern Somalia two weeks ago to fight Islamist rebels it blames for a spate of kidnappings.
In the Somali capital Mogadishu the African Union (AU) has deployed a force of 9,000 Ugandan and Burundian troops, AMISOM.
The UN Security Council has authorised AMISOM, set up in 2007, to have a total of 12,000 troops but this is also set to increase.
"As you know Uganda and Burundi are going to increase (their participation) by 4,000 and Djibouti is going to increase by 1,000," Haji told a press briefing on Kenya's Somalia intervention.
"On the 15th (of November) the heads of state of IGAD will be meeting," Haji said, referring to the Intergovernmental Development Authority, that groups together Uganda, Ethiopia, Djibouti, Kenya, Sudan and Somalia.
"That is when we'll be able to tell you concretely which countries are going to contribute," he went on.
Haji did not say where the meeting would take place, but IGAD, which is based in Djibouti, often holds its meetings in the Ethiopian capital Addis Ababa.
The summit will be preceeded by a meeting of technical experts on November 5, Haji said.
He also said a Somali delegation will visit Kenya on Sunday to discuss divisions in Somali power circles over Kenya's intervention in the south.
Kenya's military chief General Julius Karangi, speaking at the same briefing, said that after 15 days of operations, Kenya's casualties are "one dead, wounded not more than five and three still missing."
The missing include two soldiers who were kidnapped back in July and one who was lost on October 1 from a boat that was giving chase to the kidnappers of a French hostage who has since died in captivity.
Karangi denied reports that Kenya's military intervention in Somalia had been planned for several months.
"We acted as a country on the spur of the moment," he told journalists. "At no point did we plan to enter Somalia and annex territory there."
He refused to put any timeframe on Kenya's operations, saying he would pull his men out when his country no longer feels threatened by the Shebab.
"When the Kenyan government and the people of this country feel they are safe enough we shall pull back," he said, adding: "There is no timeline on it."
Officials present at the briefing dismissed earlier reports by other Kenyan officials that the government was ready to negotiate with Al Shebab.
"We will not negotiate with criminal terrorist groups," Francis Kimemia, permanent secretary at the internal security ministry said.