A roadside bomb killed five Polish soldiers in Afghanistan on Wednesday, the country's prime minister said, Poland's largest loss of life in a single incident since it joined the NATO-led coalition of foreign troops almost a decade ago.

This is very sad information for the Polish soldiers, for the whole of Poland, and especially for the families who are being informed of the fact right now, Prime Minister Donald Tusk told a news conference in Katowice, southern Poland.

The bomb had to be of a very significant power as the vehicles the Polish soldiers use are generally well-protected against this type of attack, he said.

Poland has about 2,475 troops in Afghanistan, most of them stationed in Ghazni province, southwest of the capital, Kabul. A total of 36 Polish soldiers have now been killed in Afghanistan, according to Poland's defence ministry.

Ghazni province has a heavy and growing Taliban presence but the blast hit in a village considered relatively secure, and just two kilometres from the provincial capital, Ghazni city.

Rawza village contains several historical sites and police security is seen as tight. Polish soldiers have been involved in reconstruction work on historical sites.

No civilians were wounded but the loud explosion was heard throughout the city and shattered the windows of nearby houses.

Colonel Miroslaw Ochyra from the Polish army's operational headquarters in Poland said it was unclear how the bomb had been activated because it did not explode when the first of the soldiers' armoured vehicles drove over it.

It contained an estimated 100 kg (220 lb) of explosives.

The Taliban claimed responsibility for the blast, but Ochyra said Poland would investigate that claim.

We must remember that the Taliban often claim some attacks to showcase their strength, he told Polish media.

(Additional reporting by Agnieszka Flak and Mirwais Harooni in KABUL, Gabriela Baczynska in WARSAW and Wojciech Zurawski in KATOWICE; Editing by Sanjeev Miglani and Paul Tait)