* EU's Ashton in Tehran for first time
* Next round of talks starts on March 18
* Ashton meets with six Iranian female activists
By Parisa Hafezi
ANKARA, March 9 (Reuters) - European Union foreign policy chief Catherine Ashton said on Sunday it would be "difficult and challenging" to reach a long-term nuclear deal with Iran, as diplomacy intensifies before talks between Tehran and world powers on March 18.
Ashton arrived in Tehran on Saturday for a two-day visit -the first by an EU foreign policy chief since 2008 - during which she said a wide range of issues, including bilateral ties and regional conflicts, will be discussed.
A long-lasting nuclear deal with Iran would help put an end to years of hostility between Iran and the West, ease the danger of a new war in the Middle East, and open up vast new possibilities for Western businesses.
"The interim deal is really important but not as important as a comprehensive nuclear agreement ... which is difficult and challenging," Ashton told a joint news conference with Iranian Foreign Minister Mohammad Javad Zarif, broadcast on state TV.
Iran and six world powers, represented by Ashton, struck a deal on Nov. 24 under which Tehran curbed some nuclear activities for six months in return for limited sanctions relief to allow time for a long-term agreement to be hammered out.
The deal, aimed at ending a decade-old dispute over Tehran's nuclear activities, took effect on Jan. 20.
Iran has repeatedly rejected allegations by Western countries that it is seeking a nuclear weapons capability. It says its nuclear work is for power generation and medical purposes.
The aim of the talks for the United States and its European allies is to extend the "breakout time" that Iran would need to produce enough fissile material for a nuclear bomb, and to make such a move easier to detect.
Iran has won limited relief of sanctions in exchange for curbing its most sensitive nuclear work under the deal but wants a full halt to U.S., EU and U.N. sanctions that have severely limited the oil-producing nation's economy.
"Iran is determined to reach an agreement ... We have shown goodwill and we have done our side. Now it is up to the other party to show the same goodwill and determination," Zarif said.
"With desire, commitment and willingness a comprehensive deal can be reached ... in four or five months."
The six powers do not want the talks to run beyond a six-month deadline agreed in the November deal. The late July deadline can be extended for a further six months by mutual consent.
Human rights activists are concerned that Tehran's rapprochement with the West since pragmatist President Hassan Rouhani's election in June could lead to an easing of U.N. scrutiny of its widely criticised human rights record.
At least 80 people and perhaps as many as 95 have been executed in Iran already this year, a surge in the use of the death penalty that has dampened hopes for human rights reforms under Rouhani, the United Nations said on Feb. 21.
But Ashton said "the potential of human rights dialogue in the future" was also discussed in her meeting with Zarif.
"I think it is important to ... assess for myself the level of Iran's desire for engagement and to be able to address some of those issues that ... we are particularly concerned about," Ashton said after meeting six Iranian women activists on Saturday in Tehran.
Rights activists have criticised Rouhani for failing to fulfill his election campaign promises of creating greater political and cultural freedoms.
In November, Reporters Without Borders said 10 reformist journalists and bloggers had been detained since June, while another 10 were given jail terms totalling 72 years. The authorities have closed at least five newspapers since Rouhani took office in August.
He has displayed concern over closure of pro-reform newspapers, but activists say that does not go far enough.
"It is a big mistake to shut down a newspaper on its first offence just because of an article," Rouhani said in a speech, broadcast live on state TV on Saturday.
In Jerusalem, Israeli Prime Minister Benjamin Netanyahu said he hoped Ashton had pressed Iranian officials about the ship that Israel seized in the Red Sea on Wednesday with what it described as a cargo that contained dozens of rockets sent by Iran to Palestinian militants in the Gaza Strip.
"I want to ask her if she has asked her Iranian hosts about the arms shipment to the terror organisations. And if she has not asked, why has she not done so," Netanyahu said in public remarks to his cabinet on Sunday.
"Nobody has the privilege to ignore the true, murderous actions of the regime in Tehran, and it is only appropriate that the international community will voice its opinion on the real policies of Iran and not its propaganda efforts," he said.
Iran says Israel's allegations are "baseless fabrications". (Additional reporting by Jeffrey Heller in Jerusalem; Editing by Louise Ireland)