Iran and Turkey signed cooperation agreements Thursday but failed to complete a deal to build a new natural gas pipeline - a project the United States has opposed. Washington has said any new energy deal between Iran and Turkey would send the wrong message while the West threatens new economic sanctions regarding Teheran's refusal to halt uranium enrichment. The European Union and the United States believe Iran plans to develop nuclear weapons - a claim that Teheran denies. On Thursday, President Mahmoud Ahmadinejad of Iran and Turkish President Abdullah Gul witnessed the public signing of a series of cooperation deals in a demonstration of improved ties between the Islamic Republic and the NATO ally. Ministers from both countries signed deals to combat drugs trafficking and cooperate in environment, transportation, tourism and culture. The two nations also issued a joint statement stressing their determination for further cooperation in the energy field. But Iran and Turkey failed to reach agreement on the construction of the proposed gas pipeline. "There are some snags," said Turkey's interior minister, Besir Atalay, without providing any details. Turkey's Energy Minister Hilmi Guler said: "the negotiations will continue," on the new pipeline project, which is aimed at ensuring reliable supply of Iranian natural gas to Turkey. Turkey already receives gas through an existing pipeline from Iran, but its flow often is sporadic during winters. The proposed pipeline could have an annual capacity of 40 billion cubic meters and possibly be connected to a network of US-backed pipelines carrying natural gas to Europe through Turkey, energy officials say. Relations between the two countries have improved since Turkey's Islamic-rooted leadership took power in 2002. Previous governments had for decades accused Iran of trying to export its radical Islamic regime to secular Turkey, which is aspiring to join the European Union. Ahmadinejad was holding talks with Gul during the two-day visit - his first to Turkey since he came to power in 2005. Turkey has said it is not opposed to Iran's nuclear program if it is only for civilian use to generate power. The United States also has opposed plans for Turkish investment in Iran's South Pars gas fields and the possibility of the Islamic Republic selling its gas to European markets via a US-backed pipeline through Turkey. Turkey's military regards a nuclear Iran as a possible security threat but has shared intelligence with Iran as the two countries staged simultaneous attacks against their common enemy, Kurdish guerrillas based in northern Iraq.