Portuguese Prime Minister Pedro Passos Coelho said on Wednesday there were no guarantees that the country would meet its commitment to return to the international capital markets before September 2013.

Passos Coelho said in an op-ed in the Financial Times that he was optimistic Portugal would fulfil its obligations, but called for realism and pragmatism as factors outside the government's control could play a role.

It is important to say something that will sound controversial, but is in fact not controversial at all - in an age of uncertainty there are no guarantees, he said.

Passos Coelho described Portugal's commitment to deliver on the terms and conditions of its bailout as unwavering, and dismissed suggestions of a second bailout or debt restructuring if the government's reform plan runs smoothly.

I am confident about the reform plan we have in place and our ability to return to the markets on time if we deliver it, he said.

He did concede, however, that Portugal could call for further support if impacting factors, outside the country's control, materialised.

This is why we accept that we may need to rely on the commitment of our international partners to extend further support if circumstances beyond our control obstruct our return to market financing.

He concluded: There are no guarantees and we cannot legislate for events out of our country's control. But I am convinced that we will only succeed if we deliver on the greater goal of fundamental reform, which will restore the prosperity of Portugal.

(Reporting by Stephen Mangan; editing by Christopher Wilson)