Claims for medical assistance must be submitted not more than six months after the month in which the service is rendered and shall be in the form prescribed by the commissioner, except that the commissioner may, where he finds that delay in submission of claims was caused by circumstances beyond the control of the provider, extend the period for submission of certain claims for a period not to exceed 12 months after the month in which the service was rendered; provided, however, that such limitations shall not apply to claims timely filed pursuant to Title XVIII of the federal Social Security Act of 1935, as amended, and reimbursements of such claims may be authorized by the department so long as federal financial participation in such reimbursements is available.