We are very sorry not to be able to give you a definite reply in regard to the above-mentioned matter.

上述一事恕不能给予明确答复。

He is not going to be nailed down to a definite reply

他不准备明确答复，以免受到约束。

He is not going to be nailed down to a definite reply.

他不准备明确答复,以免受到约束.

We are sorry not able to give you a definite reply in respect of the above matter.

就上述事情，我方很难给予你方肯定的答复。

We are very sorry not to be able to give you a definite reply in respect of the above matter.

就上述事情，我方歉难给予肯定的答复。