Unfortunately, I'm unable to assist at this time.

Meaning

I cannot help now.

Examples

• John: '<b>Unfortunately, I'm unable to assist at this time.</b> I have prior commitments.'
• Alice: 'Would you mind taking over this shift?'<br>
• John: 'Could you review this marketing campaign before launch?'<br>
• Alice: '<b>Unfortunately, I'm unable to assist at this time.</b> I've already reached my workload capacity.'