Tunisian Protests, by Islamist and Secular Groups, Delay Talks on Constitution CAIRO - Deadly violence and street protests in Tunisia on Wednesday postponed talks intended to end a political standoff that had thwarted completion of a new constitution in the birthplace of, and a relative bright spot in, the Arab Spring revolts. The Tunisian talks, called "the national dialogue," have captivated the Arab world with the hope that in at least one country an Islamic party and its more secular rivals might overcome the mutual distrust and antipathy that have bogged down steps toward democracy in Egypt, Libya, Syria and elsewhere in the region. But on Wednesday, the second anniversary of Tunisia's first free election, the promise appeared to have slipped away again with attacks from two fronts on the moderate Islamist governing party, from militant hard-liners on one side and secular political factions on the other. Islamist militants in Sidi Bouzid, an interior province, killed at least six security officers on Wednesday and wounded several others, apparently in an attempt to disrupt the reconciliation between the moderate Islamist governing party and its more secular opponents. At least two militants were killed in the fighting, the state news agency said. Flashes of violence by hard-line Islamists have vexed Tunisia since the ouster of the former dictator Zine el-Abidine Ben Ali in January 2011. President Moncef Marzouki, a liberal coalition partner of the Islamists, on Wednesday ordered a three-day period of national mourning. At the same time, new differences between the moderate Islamists and their more secular opponents over the basic framework of their proposed talks appeared to delay them, too. Thousands of government opponents, including leftists and union activists, marched in the capital, Tunis, to demand the swift resignation of the government of Prime Minister Ali Larayedh, of the moderate Islamic party Ennahda, as a condition of the dialogue. Tunisia's main labor union group and secular political leaders have insisted that Mr. Larayedh step down within three weeks, almost as soon as the factions can agree on a caretaker government of nonpartisan experts. But in a speech on Wednesday night that was delayed for so many hours that some opposition leaders left in impatience, Mr. Larayedh reiterated his party's position that he would resign only upon the ratification of a new constitution and the beginning of a new electoral process, not at the start of the talks or by the end of a three-week deadline. Angry opposition activists threatened a sit-in in the old city square outside the prime minister's office. Non-Islamist opposition parties vowed to suspend their participation in the planned dialogue.