Foreign Affairs Minister Kevin Rudd has written to the United Nations secretary-general and the president of the UN Security Council, demanding the president of Syria be brought before the International Criminal Court (ICC).

Mr Rudd says he is appalled by the actions of the Syrian regime and believes there are serious questions over the legitimacy of the government led by president Bashar al Assad.

He has told the National Press Club the president must be held to account.

"It is high time the Security Council now consider a formal referral of president Assad to the International Criminal Court," he said.

Australia already has sanctions in place against the country's leaders and Mr Rudd says he has taken more action.

"Today I signed off on a further list of sanctions against individual members of the regime, our third enlargement of the list of those who are currently close to the heart of the regime, including president Assad himself," he said.

Mr Rudd has also defended his hectic travel schedule as he lobbies for Australia to have a seat on the Security Council.

He used the press club speech to again outline the reasons for Australia's bid, saying the Security Council is more active and relevant on global issues than ever before.

And he says a seat would give Australia direct input into the future of Afghanistan, where hundreds of Australian troops are based.

The Opposition has questioned Mr Rudd's travel schedule and priorities, but Mr Rudd insists it is justified.

A Senate estimates inquiry heard the Foreign Minister travelled to Vietnam, Germany, the Middle East and Singapore over four days.

But he missed two regional meetings, including a conference about Australian business ties, with 350 officials in Papua New Guinea.

"Is my travel schedule heavy? Yes it is. Does it advance Australia's interests? I believe it does," Mr Rudd said.

"Will it continue? Yes it will, because that is the job of a foreign minister. If you look closely at the job description, I'm commissioned to engage with foreigners."