Former defence minister Kevin Andrews has repeated calls for Australian combat troops to join the fight against Islamic State, the day after the government confirmed it had formally declined the United States request for an increased military contribution.

This is the second time Mr Andrews - dumped from the ministry by Prime Minister Malcolm Turnbull - has spoken out in favour of troops on the ground, disagreeing with the policy of his government.

Mr Andrews told ABC radio that, while Defence Minister Marise Payne would have information he does not, a "reasonable request" should receive "the most favourable consideration".