Local officials made desperate calls to journalists to seek attention as they were unable to get hold of senior authorities for help, media reported, highlighting the disarray in security ranks.
"This morning, a group of Taliban fighters armed with heavy and light weapons launched coordinated attacks on several police checkpoints in Shah Joy district of Zabul province, killing 20 policemen," provincial governor Bismillah Afghanmal told AFP.
A district official told AFP that at least 15 others were wounded in the fighting.
Taliban militants launched their annual "spring offensive" in late April, heralding a surge in fighting as the US tries to craft a new Afghan strategy and NATO considers sending more troops to break the stalemate against the resurgent militants.
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The offensive normally marks the start of the fighting season, though this winter the Taliban continued to battle government forces. An attack on a military base in the northern city of Mazar-i-Sharif left at least 135 security forces dead last month.
The Pentagon has asked the White House to send thousands more troops to Afghanistan to break the deadlocked fight against the Taliban.