* Says violations will be met with military response
* ECOWAS delegation due to tell military it opposes coup (Adds quotes, details)
BISSAU, April 16 (Reuters) - Guinea-Bissau's military chiefs have closed the West African country's air and sea space and say all violations will be met with a "military response", defying the mounting international criticism of last week's coup.
The armed forces leadership has assumed control after soldiers arrested interim President Raimundo Pereira and former Prime Minister and presidential election front-runner Carlos Gomes Junior in an overnight putsch on Thursday.
The military said it had formed a "national transition council" with some of the country's political parties, although the main PAIGC party was not participating.
A communique from the military chiefs, read to Reuters by a military source in Bissau on Monday, said flights and vessels would not be able to enter the country's air and sea space without prior authorisation. It cited "national security" as the reason for the move.
"Non-observance of this measure will imply a military response," the communique added, without elaborating.
The warning was a tough reply to widespread strong international condemnation of the coup in the small, poor former Portuguese colony, the second military power grab in a month in West Africa following a coup in Mali on March 22.
It came as a high-level delegation from the West African regional grouping ECOWAS was preparing to fly into Bissau to deliver a tough message to the military leaders that the region considered their actions "unacceptable".
The source said the ECOWAS delegation would be authorised to enter the country and meet the military chiefs.
At the weekend, the Community of Portuguese-speaking Countries (CPLP), which counts Guinea-Bissau among its members, backed the idea of a U.N.-mandated intervention force for Guinea-Bissau to be formed with the cooperation of the African Union and the European Union.
The crumbling coastal capital Bissau was also swirling with rumours that a Portuguese warship was on its way, apparently with a mission to evacuate Portuguese and other foreign nationals.
Guinea-Bissau, which has a history of coups and whose weak governance has made it a haven for Latin American drug cartels trans-shipping cocaine to Europe, was in the middle of electing a president to replace Malam Bacai Sanha when Thursday's coup occurred. Bacai Sanha died in a Paris hospital in January after an illness. (Reporting by Alberto Dabo; Writing by Pascal Fletcher)