Azerbaijan detains election watchdog chief By Nailia Bagirova and Margarita Antidze BAKU (Reuters) - Azerbaijan on Tuesday detained an activist in what his lawyer said was political retribution for his reporting of violations in elections in which President Ilham Aliyev won a third term. A Baku court ordered Anar Mammadli, head of the independent Election Monitoring and Democracy Studies Centre, held in pre-trial detention for three months on suspicion of tax evasion and illegal business activity. Rights groups say Azerbaijan's strategic location between Russia and Iran, its oil reserves, Europe-bound energy pipelines and its role as a transit route for U.S. troops to reach Afghanistan have cushioned it from Western criticism Plans for a vital gas development that could provide Europe with an alternative to Russian supplies was signed in the former Soviet nation's capital on Tuesday. Mammadli's lawyer called the charges against his client "unfounded." "His arrest is a punishment for his centre's post-election report, where there was evidence of violations," Rashid Gajily told Reuters. Mammadli's organization was investigated by the authorities after it documented widespread electoral violations. Aliyev, in power since 2003, won a third five-year term with nearly 85 percent of the vote in the election on October 9 that international monitors also said was seriously flawed. Rights groups accuse Aliyev of curbing dissent and freedom of speech - charges dismissed by Azeri authorities who say its 9 million citizens enjoy full democratic freedoms. A spokesman for prosecutors denied the case against Mammadli was politically motivated. Amnesty International called on Western leaders on Tuesday to speak up against an arrest it said was "the latest in a series of repressive measures" by Azeri authorities. "The willingness of European leaders to turn a blind eye to Azerbaijan's continued crackdown on government critics is glaringly obvious as they endorse a new energy deal with the increasingly vengeful Aliyev regime," Denis Krivosheev, a deputy program director at the human rights group, said in a statement. British Foreign Secretary William Hague, who attended a signing ceremony of the final investment decision for the Shah Deniz II gas project in Baku, said Britain remained vocal of human rights abuses in Azerbaijan. "Azerbaijan and UK have a very close economic and political relationship, but this does not impede us from raising human rights concerns with the Azerbaijani authorities," Hague told reporters after a meeting with local civil society activists. Writing by Margarita Antidze; Editing by Alissa de Carbonnel and Alison Williams