The attacks on Tuesday in the coastal city left nine pro-government fighters dead and 82 wounded, said Reda Issa, a spokesman for forces allied with the unity government.
They took place as forces loyal to the Government of National Accord (GNA), backed by US air strikes, advanced on Sirte's central District Two as part of a three-month offensive to oust the jihadists from the city.
An IS fighter blew up his vehicle close to a group of soldiers and journalists, wounding several, said an AFP photographer.
Five of the bombers attacked using cars, one on a motorbike and three on foot, said the pro-GNA forces, which published several photos of the bombers' corpses.
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IS seized Sirte, 450 kilometres (280 miles) east of Tripoli, in June 2015 and turned it into its North African stronghold, but they now hold just a few pockets of the city.
Pro-GNA forces launched an offensive in mid-May to retake the city, which they entered on June 9, facing heavy resistance as they moved towards the centre.
The US Africa Command said Wednesday that it had carried out nine more air strikes on IS targets in Sirte on Tuesday in support of the pro-GNA forces, bringing the total number to 57 since August 1.
Last week the pro-government fighters seized a conference centre in the city used by IS as its command centre.