BAGHDAD — Bombs struck two Sunni towns at sundown Sunday just as Iraqis were preparing to break their holy day’s fast, killing 18 and wounding more than 50, officials said. Two earlier bomb blasts killed a police officer and wounded dozens of people.

The bomb attacks showed that deadly violence is still common in Iraq and in some places even worsening, seven months after the United States pulled its last troops out of the country.

Most of the bombings have borne the hallmarks of Sunni Muslim insurgents linked to Al Qaeda, targeting Shi’ites and their holy sites as well as security forces working for the Shi’ite-led government.

The two latest bombings, however, struck predominantly Sunni towns.

So far, Shi’ite militants have resisted striking back at Sunnis. It was not immediately clear if the Sunday bombings were retaliation for earlier attacks, but residents in the stricken areas raised fears of renewed sectarian conflict.

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The first sundown attack, in the town of Mahmoudiya, was the deadliest — a double bombing in which the second seemed aimed at hitting people who came to help victims of the first blast.

A car exploded around 7 p.m. in a parking lot for minibuses in the town, about 20 miles south of Baghdad. As emergency responders sprang into action, a second car blew up, according to police.

Twelve people were killed in the double blast, including two policemen, officials said; another 36 were wounded. A medic at Mahmoudiya public hospital confirmed the casualty toll.

‘‘People are worried that these attacks might ignite sectarian violence again,’’ said Ali Kamal, 41.

Syria’s bloody 17-month civil war between Sunni rebels and the regime of President Bashar Assad, a member of a Shi’ite offshoot sect, has reached the Syrian-Iraq border over the last few days.