DOHA, Qatar — Qatar agreed on Wednesday to buy seven Italian warships at a cost of nearly $6 billion in the latest example of checkbook defiance by the gas-rich country in its two-month-old feud with four neighboring Arab countries.

The military deal between Qatar and Italy, announced by the foreign ministers of both countries in Doha, Qatar’s capital, was the latest in a slew of diplomatic and economic moves suggesting that the crisis, the worst to hit the Persian Gulf countries in decades, shows little sign of abating.

Days earlier, Qatar brought its fight with Saudi Arabia, Egypt, the United Arab Emirates and Bahrain to international aviation and trade forums, and was even seen to have advanced a breathtakingly pricey soccer transfer as a means of flexing its muscles.

The measures were countered by implacable demands from the Saudi-led quartet, and offered a sense of the challenge facing Western officials, led by the Secretary of State Rex W. Tillerson, who have tried to defuse the crisis, so far in vain. On Tuesday, the State Department named Gen. Anthony C. Zinni, a four-star Marine general who retired in 2000, as a special representative to the Persian Gulf. He is expected to arrive in the region next week.